Trump’s Missile Strike on Syria and the Legality of Using Force to Deter Chemical Warfare

Trump’s Missile Strike on Syria and the Legality of Using Force to Deter Chemical Warfare Abstract The article discusses the legality of the American missile strike on Syria on 6 April 2017, that was initiated in response to the Assad regime’s alleged (repeated) use of chemical weapons in the Syrian civil war. While the academic debate about the legality under international law of the strike has primarily focused on the legality of humanitarian interventions in the traditional sense, the article argues that the strike should instead be discussed as an example of a particular form for humanitarian intervention; one that merely seeks to deter a state from using chemical weapons against civilians. This seems clear from both official US statements about the strike and from the international reactions to the military operation. The article then provides an overview of the strong international norm against chemical warfare and discusses the potential development of—and likely criteria for—a right in international customary law to use force to deter a state from using chemical weapons against civilians. It is in this vital national security interest of the United States to prevent and deter the spread and use of deadly chemical weapons.1 (President Donald J. Trump, 6 April 2017). 1. Introduction On 6 April 2017, American warships launched a series of cruise missiles at an airbase in Syria.2 The strike—that destroyed around 20 planes and killed a number of Syrian soldiers—was launched a few days after a Syrian fighter jet from the air base in question had (allegedly) dropped a chemical bomb in the town of Khan Shaykhun in Idlid Province killing dozens of people, including several children. In a statement from The White House, US President Donald J Trump stated that the American military action was a response to a ‘horrible chemical weapons attack on innocent civilians’ by ‘Syrian dictator Bashar al-Assad’ that ‘choke out the lives of helpless men, women, and children.’3 There were clear parallels between Trump’s decision to order a military strike on Assad in response to the regime’s use of chemical weapons and then-president Barack Obama’s threat of using military force against the Assad-government in 2013 after a chemical attack by Syrian forces in Gouta near the Syrian capital of Damascus.4 A year prior to Obama’s threat, the president had infamously declared that any use of chemical weapons in the Syrian civil war constituted a ‘red line’ the crossing of which would have ‘enormous consequences’.5 Obama never followed-up on his threats of using force against Assad and the crisis in 2013 was instead resolved when the United Nations Security Council—on a sudden Russian initiative—became involved and on 27 September 2013, adopted a resolution demanding that Syria cooperated with the Organization for the Prohibition of Chemical Weapons (OPCW) and destructed all its chemical weapons.6 Two weeks prior to that, Syria had rushed to sign the 1993 Chemical Weapons Convention to which it had not previously been a party.7 When it deposited its instrument of accession to the Convention, the Syrian Government declared that it would ‘comply its stipulations and observe them faithfully and sincerely’.8 Events since the 2013-crisis has shown, however, that the Syrian regime did not fully cooperate with the OPCW and in both 2015 and 2016, the Security Council condemned the continued use of chemical warfare in the Syrian war, including by the Syrian Government.9 The consistent use of chemical weapons in Syria has been confirmed by a range of OPCW fact-finding missions.10 In June 2017, one such mission concluded that chemical weapons had indeed been used in the attack in Khan Shaykhun in April 2017.11 On 26 October 2017, an OPCW—UN Joint Investigative Mechanism (JIM) created by the Security Council to identify those involved in the use of chemical weapons in Syria,12 stated that it was ‘confident’ that the Syrian Government was ‘responsible for the release of sarin at Khan Shaykhun on 4 April 2017’.13 The Trump Administration has not put forward any legal justification for the military operation against Syria but the academic debate about the legality of the operation has primarily been concentrated on the by now well-known arguments for and against the legality of humanitarian intervention without a mandate from the UN Security Council. So when evaluating the American strike, legal experts have for the most part debated if a state like the United States is entitled to use force in a state like Syria in the absence of an authorization from the United Nations Security Council in order to try to bring a halt to an unfolding humanitarian crisis. Here, too, the events surrounding the American strike on Syria resemble the situation in the 2013-crisis where Obama’s threat to use force in Syria ignited a heated debate about the legality of unilateral humanitarian interventions.14 The purpose of the present article is two-fold. First, it will argue that the American strike on Syria does not fit very well with our traditional understanding of what a humanitarian intervention is. Both the political justifications offered by the US Government as well as the international reaction strongly indicate that the military operation should instead be perceived of as having the more limited purpose of seeking to deter the Syrian regime from continuing its use of chemical weapons against civilians in the civil war. Secondly, the article will build upon that conclusion and ask what it would take for a state to be entitled to use non-UN sanctioned military force against another state to deter it from resorting to chemical warfare against civilians. Is such a right on the horizon? What might it look like? The article concludes that although a right to use non-UN sanctioned force to deter chemical warfare against civilian is not yet established, the positive international reaction to the US strike on Syria could indicate that such a right may be in the early stages of creation. The analysis begins in Section 2 with a brief overview of the well-known discussion of a right to humanitarian intervention without a mandate from the Security Council and an explanation of why the American strike on Syria does not fit the traditional category of a humanitarian intervention. Section 3 provides an overview of the strong international norm against chemical warfare before Section 4 discusses the legality of the American strike and the likelihood of the emergence of a right to use force to deter the use of chemical weapons. Section 5 contains a short conclusion. 2. Humanitarian intervention? Any analysis of the legality under international law of using force against another state takes its point of departure in the 1945 Charter of the United Nations. The structure of the Charter is well-known to most readers of this journal. The central provision in the Charter is Article 2 (4) that contains an overall prohibition on the use of force whereby all member states ‘shall refrain in their international relations from the threat or use of force against the territorial integrity or political independence of any state, or in any other manner inconsistent with the Purposes of the United Nations’. According to the ICJ, the prohibition in Article 2(4) is also reflected in customary international law.15 Importantly, Article 2(4) covers all possible uses of force including the use of force for humanitarian purposes.16 The Charter entrusts the Security Council with the primary responsibility for the maintenance of international peace and security and to that end provides the Council with wide-ranging powers, including the competence to authorize the use of force if required to restore or uphold international peace.17 In addition, Article 51 stipulates that states retain their ‘inherent’ right of individual or collective self-defence if an armed attack occurs until the Security Council has taken measures necessary to maintain international peace and security. The Charter system for using force is therefore essentially fairly straightforward. States can only use force against another state if authorized by the Security Council or if compatible with a right to self-defence.18Several attempts has nevertheless been made to argue for the legality of using force in another state for the purposes of putting a halt to widespread atrocities against a local population in the absence of a mandate from the Security Council. While there is no need here to re-enact the lengthy debate about the legality of such unilateral humanitarian interventions,19 it is worth noting that most proponents of a right to humanitarian intervention derive the right from customary international law. Support is primarily found in NATO’s non-UN sanctioned humanitarian intervention in Kosovo in 1999.20 However, a closer look at the events in 1999 reveals that the majority of states that participated in the Kosovo intervention were actually very reluctant to officially argue that their actions were lawful under international law. In fact, most of the states preferred to claim that their intervention was probably unlawful but nevertheless legitimate. To date, only the United Kingdom21, Belgium22 and Denmark23 have officially argued that non-UN-sanctioned use of force for humanitarian purposes can be compatible with international law. The United States is among the states that have yet to claim that a non-UN sanctioned humanitarian intervention can be compatible with international law. So far, Washington seems to prefer the ‘unlawful but legitimate’ position.24 The closest the United States has come to arguing for a right to unilateral humanitarian intervention was an August 2013 statement in which president Obama’s White House Counsel noted that a potential upcoming military operation against Syria without backing from the United Nations in response to Syria’s use of chemical weapons would be ‘justified and legitimate under international law’ even though it would not fit ‘a traditionally recognized legal basis under international law’.25 The American reluctance to go ‘all inn’ in the debate about humanitarian intervention has been criticized by, among others, former legal adviser in the US State Department Harold Hongju Koh. Koh was among those who argued for the legality of non-UN-sanctioned humanitarian intervention in Syria in 2013.26 In 2016, Koh identified a range of criteria that he considers should guide the determination of the legality of humanitarian uses of force not sanctioned by the Security Council.27 In his defense of non-UN-sanctioned humanitarian interventions, Koh links such an alleged right to the doctrine of Responsibility to Protect (R2P).28 That is remarkable because it is pretty clear that the R2P doctrine does not justify using force in the absence of a mandate from the Security Council.29 In fact, the 2005 UN World Summit Outcome Document that Koh refers to in his 2016 article explicitly states that any ‘collective action’ to enforce the doctrine must be taken ‘through the Security Council, in accordance with the Charter, including Chapter VII’.30 Despite the various attempts to argue for a right to use force for humanitarian purposes without a mandate from the UN Security Council, it is hard to find support for the claim that customary international law has progressed to a stage that it would allow such use of force.31 Proponents of a right to unilateral humanitarian intervention tend to ignore the strong non-Western opposition to humanitarian interventions. As noted in the introduction, the United States has not offered any legal justification for the military operation against Syria but the majority of scholars that have voiced their opinion about the legality of the operation appear to consider the strike as an example of a non-UN sanctioned humanitarian intervention. For the most part, therefore, the scholars also find that the strike was incompatible with international law.32 But the present author is not convinced that the American strike on Syria should be considered as a humanitarian intervention—at least not in a conventional sense. While it is true that the US operation was initiated in response to atrocious acts committed by the Syrian regime against the Syrian civilian population, the decision to launch the strike does not appear to be motivated by an overarching desire to put a halt to the war in Syria and thus to stop the suffering of Syrian civilians as such. Rather, statements by the Trump-administration clearly indicate that the strike was motivated by a less ambitious (some might say cynical) attempt to merely stop those parts of the human atrocities that are perpetrated by chemical weapons. In his political justification for the missile strike, President Trump explicitly linked the need to respond to the ‘horrible chemical weapons attack on innocent civilians’ to the ‘vital national security interest of the United States to prevent and deter the spread and use of deadly chemical weapons’. Trump also stated how there ‘can be no dispute that Syria used banned chemical weapons, violated its obligations under the Chemical Weapons Convention, and ignored the urging of the U.N. Security Council’.33 The US National Security Advisor, General McMaster, stated that the strike on Syria was meant to ‘deter the continued use, because there’s been a pattern of the abuse of chemical weapons by the Assad regime and his mass murder attacks against innocent civilians … The objective was to send a very strong political message to Assad.’34 Similar statements came from the American Secretary of Defence, General Mattis, who noted that the purpose of the strike was to ‘deter future use of chemical weapons and to show the United States will not passively stand by while Assad murders innocent people with chemical weapons, which are prohibited by international law and which were declared destroyed.’35 The international reaction to the missile strike also strongly indicates that the operation should be perceived of as an attempt to deter the Assad-regime from continuing its use of chemical weapons in the Syrian civil war and not as a humanitarian intervention in the classic sense. As we shall return to in Section 4, the overwhelmingly positive political reactions to the American use of force were for the most part explicitly tied to Assad’s unlawful use of chemical weapons. Rather than discussing if the American strike on Syria was compatible with a potential right to humanitarian intervention without a Security Council mandate, the legal analysis of the operation should therefore focus on the legality of using non-Council-sanctioned force to deter a state from engaging in chemical warfare. That is the focus of the remainder of the article. 3. The norm against chemical warfare There is a very strong international norm against any use of chemical weapons in armed conflict.36 In his examination of the origins of what he calls the ‘chemical weapons taboo’, Richard Price notes how the objection to chemical warfare originally seemed to be derived from the practical difficulty of controlling the release of chemical substances and the accompanying risk that both combatants and civilians would be exposed to the chemicals. Using chemical weapons was hereby deemed to be incompatible with the fundamental law of war principle of distinction that requires parties to a conflict not to use weapons that cannot distinguish between military and civilian objectives.37 But the norm against chemical warfare also appears to be tied to an ancient ethical objection to using poison as a weapon in war.38 It seems that chemical warfare violates basic norms of ‘civilized’ behaviour regardless of against who the chemical weapons are used.39 In the seminal Tadíc case, the International Criminal Tribunal for the former Yugoslavia (ICTY) referred to chemical weapons as an example of a weapon deemed inherently inhumane.40 The earliest prohibition in international law against chemical warfare is found in a declaration adopted at the 1899 Peace Conference in Haag where the contracting parties agreed to ‘abstain from the use of projectiles the sole object of which is the diffusion of asphyxiating or deleterious gases.’41 Following the widespread use of chemical weapons in the trenches in World War I,42 the 1925 Protocol for the Prohibition of the Use in War of Asphyxiating, Poisonous or Other Gases, and of Bacteriological Methods of Warfare was adopted at a conference in Geneva. The Protocol—that entered into force in 1928—prohibits the use of biological and chemical warfare, and it served as the primary legal instrument for the prohibition of chemical weapons until the adoption on 13 January 1993, of the Convention on the Prohibition of the Development, Production, Stockpiling and Use of Chemical Weapons and their Destruction. As its name reveals, this Chemical Weapons Conventions (CWC) prohibits not only the use of chemical weapons in times of armed conflict but also their development, storing, as well as military preparations for chemical warfare.43 The CWC obliges states to destroy chemical weapons they may be in possession of, to dismantle their facilities for producing chemical weapons44 and to comply with a verification and inspection regime.45 The Convention created the Organization for the Prohibition of Chemical Weapons (OPCW) in The Hague, the Netherlands, where all state parties meet in annual conferences to discuss matters and issues that fall within the scope of the Convention. The OPCW is headed by an Executive Council consisting of 41 members. By November 2017, the CWC—that entered into force in 1997—had 192 parties.46 Egypt, North Korea and South Sudan have neither signed not ratified the convention. Israel has signed the Convention but not (yet) ratified it. It is widely held that the prohibition against using chemical weapons reflects customary international law in both international and non-international armed conflicts.47 As already noted, in Tadíc, the ICTY referred to chemical weapons as an example of a weapon that is considered inhumane in all types of armed conflict.48 The use of chemical weapons in an international armed conflict is also listed in the 1999 Rome Statute as a war crime within the jurisdiction of the International Criminal Court (ICC).49 The obligation not to use chemical weapons would also appear to constitute an obligation erga omnes that is owed to the ‘the international community as a whole’.50 The strong norm against chemical warfare is also reflected in resolutions adopted by the UN Security Council. On 28 April 2004, the Council adopted Resolution 1540 concerning non-proliferation of weapons of mass destruction. The resolution begins by affirming ‘that the proliferation of … chemical … weapons, as well as their means of delivery, constitutes a threat to international peace and security’. The Resolution was adopted pursuant to Chapter VII of the Charter and it contains a range of obligations aimed at preventing the spread of such weapons. It also created an ad hoc committee—the ‘1540 Committee’—for purposes of monitoring the implementation of the resolution. Despite the long-existing prohibition on using chemical weapons in armed conflict there are numerous examples of (prohibited) chemical warfare.51 Up until the chemical attacks in the civil war in Syria, the best-known recent example is Iraq’s campaign of chemical warfare in its war against Iran (1980–1988) and its extensive use of chemical gas against its own Kurdish population in the so-called ‘Anfal Campaign’ (1986–1989) in the North of Iraq.52 In one attack alone, in the town of Halabja, chemical gases killed an estimated 5000 Kurdish civilians. Iraq’s use of chemical weapons against the Kurds were condemned by many states53 and in June 2007, the ‘mastermind’ of the chemical attacks against the Kurds—Ali Hassan Al-Majid (also known as ‘Chemical Ali’)—was found guilty of genocide and sentenced to death by an Iraqi court.54 In 2007, insurgents and operatives of Al Qaida in Iraq (AQI) attempted to release chlorine gases in Improvised Explosive Devices (IEDs) in truck bombs in the war in Iraq.55 Terrorist organizations have also used chemical substances outside armed conflict. In 1994 and 1995, a Japanese sect (Aum Shinriko) released Sarin nerve gas in the Japanese cities of Matsumoto and Tokyo, killing 13 people.56 In addition, from its sanctuary in Afghanistan, Al Qaida actively sought to develop chemical weapons for potential use in terrorist attacks in the late 1990s.57 As mentioned in the introduction, the Security Council became involved in the crisis following the 2013 Gouta-attack in Syria when US President Obama refrained from moving ahead with the threatened military operation against Assad and instead sought to find a diplomatic solution to the crisis. In Resolution 2118, the Council on 27 September 2013 responded to the Gouta-attack by condemning the use of chemical weapons in Syria and reaffirmed ‘that the proliferation of chemical weapons, as well as their means of delivery, constitutes a threat to international peace and security’ as well as ‘a serious violation of international law’. The Council also stressed how ‘those responsible for any use of chemical weapons must be held accountable’ and it welcomed the establishment by the UN Secretary-General of a Mission to Investigate Allegations of the Use of Chemical Weapons in Syria. On 14 September 2013, Syria had signed the CWC and promised to comply with the provisions of the Convention even though it would only become formally binding on that state 30 days later.58 In Resolution 2235, the Security Council on August 7, 2015, noted ‘with outrage that civilians continue to be killed and injured by toxic chemicals as weapons’ in Syria and stressed again ‘that those individuals responsible for any use of chemical weapons must be held accountable’. The Council established an OPCW–UN Joint Investigative Mechanism to identify those who are involved in the use of chemical weapons in Syria where a fact-finding mission by the OPCW has determined that chemical weapons has been used.59 Since its creation, the Mechanism has published seven reports that have concluded that both the Syrian Armed Forces as well as the Islamic State in Iraq and Levant (ISIL) had used chemical weapons in the war in Syria.60 As noted in the introduction, in October 2017, the Mechanism concluded that it was the Syrian Government that was behind the chemical attack in Khan Shaykhun in April 2017.61 The Council extended the mandate of the Mechanism for one year in November 201662, but in October 2017 a Russian veto prevented the Security Council from reaching agreement on a further extension.63 The international reaction to the American missile strike on Syria in April 2017 illustrates how strong the norm against chemical warfare is. Thus, with the exception of Russia64 and Iran,65 states have generally offered solid political support for President Trump’s decision to use military force against the Assad-regime in response to its chemical attacks in the civil war. Shortly after the strike, a spokesperson from the British Government stated that the United Kingdom ‘fully supports the US action, which we believe was an appropriate response to the barbaric chemical weapons attack launched by the Syrian regime, and is intended to deter further attacks’.66 In a joint statement, the French President and the German Chancellor stated that ‘President Assad alone carries responsibility for these developments’ in light of his ‘repeated use of chemical weapons and his crimes against his own people’.67 On 29 May 2017, in response to a question about the war in Syria, French President Emmanuel Macron (then newly elected) also stated that any ‘use of chemical weapons would results in reprisals and an immediate riposte, at least where France is concerned’.68 Immediately after the strike, the President of the European Council, Donald Tusk, tweeted that the operation ‘show much needed resolve against barbaric chemical attacks’.69 NATO’s Secretary-General Jens Stoltenberg noted how ‘NATO has consistently condemned Syria’s continued use of chemical weapons as a clear breach of international norms and agreements’.70 Similar political support coupled with condemnation of Assad’s use of chemical weapons came Spain,71 Italy,72 Australia,73 Israel,74 Japan,75 Saudi Arabia,76 Jordan and Turkey.77 Even China offered its political support to the missile strike without noting that the strike seems hard to reconcile with the UN Charter.78 4. A right to use force to deter chemical warfare against civilians? At the outset it is worth noting that from the perspective of international law, the American strike on Syria in April 2017 can be approached from different angles. Thus, before turning to the discussion of a potential right to use force to deter chemical weapons in customary international law, it is necessary to briefly touch upon two other possible legal justifications for the American strike. The first relates to the issue of countermeasures. The American strike could be perceived of as a response to Syria’s unlawful use of prohibited weapons and thus its violation of international law. The United States was not injured by Syria’s unlawful use of chemical weapons but a non-injured state may be entitled to invoke the responsibility of another state ‘if the obligation breached is owed to the international community as a whole’.79 In Barcelona Traction, the ICJ famously stated that a state may have certain obligations not just to another state but towards ‘the international community as a whole’ and that all states have a legal interest in the protection of such rights.80 As noted in the previous section, Syria’s obligation not to use chemical weapons in armed conflict could very well be an obligation erga omnes that all states, including the United States, has an interest in protecting. One of the ways whereby a state may respond to another state’s internationally wrongful acts is by taking countermeasures in order to bring the wrongful acts to a halt. It is not at present clear if—and if so, how—a non-injured state may resort to countermeasures in response to a breach of international law.81 What is certain, however, is that armed countermeasures are prohibited.82 The American strike on Syria cannot therefore possibly be justified as a lawful countermeasure. A second alternative justification is a plea of necessity. As a concept under international law, necessity relates to those rare cases where the only way for a state to safeguard an essential interest threatened by a grave and imminent peril is, for the time being, not to perform some other international obligation of lesser weight or urgency.83 However, as discussed at greater length elsewhere,84 necessity does not appear to a valid defence to justify violations of the prohibition on the use of force in Article 2(4) of the UN Charter. Most importantly, necessity is unavailable if the international obligation in question ‘excludes the possibility of invoking necessity’.85 While the Charter does not explicitly mention necessity it seems logical to conclude that the Charter is the exclusive source on the international legal regulation of interstate force in the sense that it rules out the invocation of necessity.86 Thus, aside from the powers of the Security Council, the right to self-defence is the only legal defence to a violation of the prohibition on the use of force under international law. It should also be noted that necessity cannot be invoked to justify violating a rule of a jus cogens character. Although one could certainly discuss if the entire prohibition on the use of force in the UN Charter is really of a jus cogens nature, it does seem to be the position by the ICJ87 and the International law Commission.88 This, then, brings us to the status in customary international law. Professor Michael N Schmitt and Lt Col Chris Ford have argued that the American strike on Syria could pave the way for changes to the international regulation of the use force. On 8 April 2017, they noted that we may be: witnessing … the slow and rather painful birth of a nascent right in customary international law allowing States to act forcefully to put an end to the use of particularly repugnant weaponry against a civilian population, or perhaps even one countenancing forceful State responses to other egregious forms of terrorizing and massacring civilian populations in other countries.89 The emergence of a right in customary international law to use force to deter the use of chemical weapons against civilians requires the establishment of a general practice among states that is accepted by those states as legally relevant (opinio juris).90 At present, state practice is far too scarce to lend much support to the conclusion that international law should have changed sufficiently to accommodate the kind of use resorted to by the United States. Thus, despite the positive political reactions to the American strike on Syria, it is clear that the missile strike on Syria was incompatible with international law. This does not preclude, of course, that Schmitt and Ford may not be correct in noting that the law could be gradually moving towards the creation of a right in customary international law to use force to deter chemical warfare. What would the contours of a potential right to use force to deter chemical warfare look like? In practice, of course, the decisive factor will be subsequent state practice as well as the international reactions thereto. But a sensible place to start would be to re-examine the criteria for (alleged) lawful non-UN sanctioned humanitarian intervention that have been put forward by the British and Danish Government. According to the UK and Denmark,91 using force for humanitarian purposes will be compatible with international law if three conditions are fulfilled: (i) ‘there is convincing evidence, generally accepted by the international community as a whole, of extreme humanitarian distress on a large scale, requiring immediate and urgent relief’; (ii) ‘it must be objectively clear that there is no practicable alternative to the use of force if lives are to be saved’; and (iii) ‘the proposed use of force must be necessary and proportionate to the aim of relief of humanitarian need and must be strictly limited in time and scope to this aim’.92 If one were to build on these criteria, the relevant factors for determining the potential future legality of using force to deter a state from using chemical weapons against civilians could look like the following. First, the use of force must be a response to convincing evidence that a state has used chemical weapons against civilians in an armed conflict. One could argue, of course, that a potential right to use force to deter chemical warfare ought to be relevant to all uses of chemical weapons and not only to those instances where chemical weapons has been used against civilians/non-combatants. After all, the legal ban on chemical weapons covers all use of such weapons in armed conflict. Schmitt and Ford appear to limit a potential right to use force to chemical warfare against civilians. This seems sensible because the international condemnation of the chemical attacks in Syria has so far focused on the civilian casualties of using such weaponry. In addition, since a potential right to use force to deter a state from using chemical weapons would be an exception to the overall ban on the use of force in Article 2(4) such an exception should be construed as narrow as possible. This also speaks in favour of limiting a potential emerging customary right to those instances where chemical weapons are used in a non-international armed conflict, such as the conflict in Syria. Secondly, it must be objectively clear that there is no realistic alternative to the use of force if the chemical warfare is to be brought to a halt. Using force without a mandate from the Security Council must always be last resort and any realistic non-forcible avenues for pressuring a state to halt its use of chemical weapons must have been exhausted. To be perceived as politically legitimate, a decision to use force should be supported by as many states as possible, preferably by a regional organization. In that regard it is worth noting that the Trump Administration did not appear to have tried to build a broad international coalition behind its April 6 decision to launch a missile strike against the Assad regime. Washington did not seek, for instance, to involve NATO before they resorted to using force against Syria. The third and final condition is that the use of force is proportionate to the aim of deterring the state that has used chemical weapons from continuing its use of such weapons and strictly limited in time and scope to this aim. This requirement of proportionality will in most cases probably demand that there are indications that continuing uses of chemical weapons are likely. When compared to a less clearly defined and broader right to humanitarian intervention in the traditional sense, a limited right to use force to deter a state from continuing to use chemical weapons against civilians would be fairly clearly demarcated and thus, one would hope, not as prone to potential abuse as the alleged—broader—right to humanitarian intervention as such. 5. Conclusion The American missile strike on Syria was not a humanitarian intervention in the classic sense but a use of force that sought to deter Syria from continuing its chemical warfare against civilians in the civil war in Syria. The American strike was incompatible with international law. It is too early to tell is such an instance of force may one day become lawful under customary international law but the positive political reaction to the strike illustrates that the norm against the use of chemical warfare is very strong. Footnotes 1 D Trump, ‘Statement by President Trump on Syria’ (6 April 2017) <www.whitehouse.gov/the-press-office/2017/04/06/statement-president-trump-syria> accessed 30 November 2017. 2 Michael R Gordon, Helene Cooper and Michael D Shear, ‘Dozens of U.S. Missiles Hit Air Base in Syria’, New York Times (New York, 6 April 2017) <www.nytimes.com/2017/04/06/world/middleeast/us-said-to-weigh-military-responses-to-syrian-chemical-attack.html?_r=0> accessed 2 March 2018. 3 See (n 1). 4 For more, see United Nations Mission to Investigate Allegations of the Use of Chemical Weapons in the Syrian Arab Republic, Report on the Alleged Use of Chemical Weapons in the Ghouta Area of Damascus on 21 August 2013, 16 September 2013, A/67/997-S/2013/553. For a discussion of some of the international law implications of the Syrian use of chemical weapons in 2013, see also Mika Hayashi, ‘Reacting to the Use of Chemical Weapons: Options for Third States’ (2014) 1(1) JUFIL 80–121. 5 Mark Landler, ‘Obama Threatens Force Against Syria’, New York Times (20 August 2012) <www.nytimes.com/2012/08/21/world/middleeast/obama-threatens-force-against-syria.html> accessed 2 March 2018. 6 UNSC Res 2118 (27 September 2013), para 4, 6 & 7. 7 The Convention entered into force for Syria on 14 October 2013, see <www.opcw.org/about-opcw/member-states/member-states-by-region/asia/member-state-syria/> accessed 2 March 2018. 8 See OPCW, Executive Council, Decision Destruction of Syrian Chemical Weapons, EC-M-33/DEC.1, 27 September 2013, available at <www.opcw.org/fileadmin/OPCW/EC/M-33/ecm33dec01_e_.pdf> (accessed 2 March 2018). 9 UNSC Res 2235 (7 August 7 2015) and UNSC Res 2319 (17 November 2016). 10 For an overview of OPCW fact-finding missions in Syria, see www.opcw.org/special-sections/syria/fact-finding-mission-reports/> accessed 2 March 2018. 11 Report of the OPCW Fact-Finding Mission in Syria Regarding an Alleged Incident in Khan Shaykhun, Syrian Arab republic April 2017, S/1510/217, 29 June 2017. 12 Res 2235 (n 9) para 5. 13 Seventh Report of the Organization for the Prohibition of Chemical Weapons-United Nations Joint Investigative Mechanism, 10. See S/2017/904, 26 October 2017. 14 For a discussion, see A Henriksen and M Schack, ‘The Crisis in Syria and Humanitarian Intervention’ (2014) 1(1) JUFIL 122–47. 15 Military and Paramilitary Activities in and against Nicaragua (Nicaragua v United States of America). Merits, Judgment ICJ Reports 1986, 14, paras 188–90. 16 Y Dinstein, War, Aggression and Self-Defence (5th edn, Cambridge University Press) 90; I Brownlie, International Law and the Use of Force by States (OUP 1963) 265–8; T Franck, Recourse to Force: State Action Against Threats and Armed Attacks (CUP 2002) 12; A Randelzhofer, ‘Article 2(4)’ in B Simma (ed) The Charter of the United Nations: A Commentary (2nd edn, OUP 2002) 123. 17 See art 42 of the UN Charter. 18 Please note that valid consent by a territorial state to the use of force on its territory by another state precludes the wrongfulness of the latter state’s acts as long as these remains within the limits of that consent, sea art 20 of the International Law Commission’s 2001 draft articles on Responsibility of States for Internationally Wrongful Acts, see GA Res 56/83 of 12 December 2001, corrected by document A/56/49(Vol I)/Corr 4. 19 For a comprehensive debate, see Henriksen & Schack (n 14). 20 ibid, 138–42. 21 The United Kingdom was the first state to officially argue that an intervention like the one in Kosovo could be legal as an ‘extraordinary measure to prevent an overwhelming humanitarian catastrophe’, see S/PV.3988, 24 March, 12. The British repeated its claim in 2013 in connection with the prospects of a potential US-led military action against Syria in response to the August 2013 Gouta chemical weapons attack, see Prime Minister’s Office, Chemical Weapon Use by Syrian Regime - UK Government Legal Position (29 August 2013) <www.gov.uk/government/publications/chemical-weapon-use-by-syrian-regime-uk-government-legal-position/chemical-weapon-use-by-syrian-regime-uk-government-legal-position-html-version> accessed 2 March 2018. 22 Belgium argued for the international legality of the 1999 intervention in the course of proceedings before the International Court of Justice (ICJ) in a case brought against NATO members by the former Yugoslavia, see Legality of Use of Force (Serbia and Montenegro v Belgium), Oral Proceedings, Public sitting, 10 May 1999, 12. 23 In 2013, Denmark supported the British legal position that humanitarian intervention without an authorization from the Security Council could be lawful, see ‘Overordnede principielle overvejelser om det folkeretlige grundlag for en evt. militær operation i Syrien’, in Udenrigspolitisk Nævn, bilag 298, alm del, 2012–2013. See also Danish Ministry of Defence, Militærmanual om folkeret for danske væbnede styrker i internationale militære operationer (September 2016) 16. 24 The American justification for the intervention in Kosovo is available in Michael J Matheson, ‘Justification for the NATO Air Campaign in Kosovo, (2000) 94 ASILP 301. For an overview of the American position vis-à-vis humanitarian intervention, see also Harold Hongju Koh ‘Address: The War Powers and Humanitarian Intervention’ (2016) 53 Houston Law Review 971–1033. 25 See Charlie Savage, ‘Obama Tests Limits of Power in Syrian Conflict’ New York Times (8 September 2013) <www.nytimes.com/2013/09/09/world/middleeast/obama-tests-limits-of-power-in-syrian-conflict.html> accessed 2 March 2018. 26 Harold Hongju Koh, ‘Syria and the Law of Humanitarian Intervention (Part II: International Law and the Way Forward)’ (Just Security, 2 October 2013) <www.ejiltalk.org/syria-and-the-law-of-humanitarian-intervention-part-ii-international-law-and-the-way-forward/> accessed 30 November 2017. 27 Koh (2016) (n 24) 1011. 28 ibid 976, 1004–1010 and 1032. 29 See also Henriksen & Schack (n 14) 128–33. 30 GA Res 60/1, World Summit Outcome Document, 24 October 2005, s 139. See also the statement by the UN Secretary-General in UN Document, A/63/677, 2009, para 3. 31 See the discussion and references in Henriksen & Schack (n 14) 128–33 32 For an overview of academic positions, see Ryan Goodman, ‘What Do Top Legal Experts Say About the Syria Strikes?’ (Just Security, 7. April 2017) <www.justsecurity.org/39712/top-legal-experts-syria-strikes/> accessed 30 November 2017; John Bellinger, ‘What was the Legal Basis for the U.S. Air Strikes Against Syria?’ (Lawfare, 6 April 2017) <www.lawfareblog.com/what-was-legal-basis-us-air-strikes-against-syria> accessed 30 November 2017; Marty Lederman, ‘Why the Strikes Against Syria Probably Violate the U.N. Charter and (therefore) the U.S. Constitution’ (Lawfare, 6 April 2017) <www.justsecurity.org/39674/syrian-strikes-violate-u-n-charter-constitution/> accessed 30 November 2017; Ashley Deeks, ‘How Does the Syria Situation Stack up to the “Factors” that Justified Intervention in Kosovo?’ (Lawfare, 7 April 2017) <www.lawfareblog.com/how-does-syria-situation-stack-thefactors-justified-intervention-kosovo> accessed 30 November 2017. For a more positive assessment, see Harold Hongju Koh, ‘Not Illegal: But Now the Hard Part Begins’, (Just Security, 7 April 2017) <www.justsecurity.org/39695/illegal-hard-part-begins/> 30 November 2017. 33 See (n 1). 34 ‘Exclusive: General H.R. McMaster on decision to strike Syria’, Fox News, 9 April 2017 <www.foxnews.com/transcript/2017/04/09/exclusive-general-h-r-mcmaster-on-decision-to-strike-syria.html> acceessed 2 March 2018. 35 Statement by Secretary of Defense Jim Mattis on the U.S. Military Response to the Syrian Government’s Use of Chemical Weapons, 10 April 2017 <www.defense.gov/News/News-Releases/News-Release-View/Article/1146758/statement-by-secretary-of-defense-jim-mattis-on-the-us-military-response-to-the/> accessed 2 March 2018. 36 Richard Price, ‘A Genealogy of the Chemical Weapons Taboo’ (1995) 49 International Organizations, Winter 73–103. Chemical warfare agents consist of manmade toxic chemicals like chlorine, phosgene and sarin nerve gas. For an overview of the international regulation of chemical weapons, see William H Boothby, Weapons and the Law of Armed Conflict (OUP 2009) 129–39. For an analysis of the threat of chemical weapons, see Jonathan B Tucker, ‘The Future of Chemical Weapons’ (2009/2010) The New Atlantis, Fall/ Winter 3–29. [AQ] 37 Price (n 36) 82–3. 38 See also the 1874 Brussel Declaration that sought to outlaw the use of poison or poisoned weapons and the 1880 Manual on The Laws of War on Land, Oxford. 39 The prohibition against using chemical weapons was not always deemed applicable in wars against ‘uncivilized’ nations or peoples, see the references in Boothby (n 36) 10. 40 Prosecutor v Dusko Tadic, Decision on the Defence Motion for Interlocutory Appeal on Jurisdiction, IT-94-1 (2 October 1995), paras 120–24. 41 Declaration (IV, 2) concerning Asphyxiating Gases. The Hague, 29 July 1899. 42 Germany was the first state to use chemical weapons in World War One (at Ypres in April 1915) and by the end of the war an estimated 90,000 people has been killed by toxic agents, see Tucker (n 36) 4. 43 CWC art I. 44 Ibid, art I (2–4). 45 Ibid, art IV. 46 OPWC, Status of Participation in the Chemical Weapons Convention as at 17 October 2015 <www.opcw.org/about-opcw/member-states/> accessed 2 March 2018. 47 Jean-Marie Henckaerts & Louise Doswald-Beck, Customary International Humanitarian law: Volume I: Rules, (CUP 2005), see Rule 74. See also Boothby (n 36) 137–38 and Sandesh Sivakumaran, The Law of Non-International Armed Conflict (OUP 2012) 394. 48 Tadic (n 40) 49 Rome Statute art 82(b) (xviii). 50 Barcelona Traction, Light and Power Company, Limited, Judgment, ICJ Reports 1970, 3, para 33. The ICJ has states that certain obligations under international humanitarian law may be obligations erga omnes, see Legal Consequences of the Construction of a Wall in the Occupied Palestinian Territory, Advisory Opinion, ICJ, Reports 2004, 136, para 155–7. 51 See the short overview in John Kierulf, Disarmament (DJØF Publishing 2017) 135–37. 52 For an elaborate and convincing account of ‘Anfal’, see Human Rights Watch, Genocide in Iraq, The Anfal Campaign Against the Kurds (July 1993) <www.hrw.org/reports/1993/iraqanfal/> accessed 2 March 2018. 53 See the references cited in Tadíc (n 40). 54 CNN, ‘Chemical Ali’ sentenced to hang (14 June 2007) <http://edition.cnn.com/2007/WORLD/meast/06/24/iraq.ali/> accessed 2 March 2018. 55 Tucker (n 36) 14. 56 Kierulf (n 51) 136. 57 Tucker (n 36) 23–24. 58 See the reference in UNSC Res 2118 (n 6). 59 See resolution 2235 (n 8), para 5. 60 See, inter alia, Third Report of the Organization for the Prohibition of Chemical Weapons-United Nations Joint Investigative Mechanism, S/2016/738/Rev.1, 24 August 2016 and Seventh Report of the Organization for the Prohibition of Chemical Weapons-United Nations Joint Investigative Mechanism, S/2017/904, 26 October 2017. 61 See (n 13). 62 Res 2319 (n 9). 63 UN News Centre, ‘Security Council Fails to Extend Mandate of Panel Investigating Use of Chemical Weapons in Syria’, 24 October 2017 <https://news.un.org/en/story/2017/10/569212-security-council-fails-extend-mandate-panel-investigating-use-chemical-weapons> accessed 2 March 2018. 64 Madison Park, ‘Who's with the US on Syria Strike and who isn't’ CNN (9 April 2017) <http://edition.cnn.com/2017/04/07/world/syria-us-strike-world-reaction/> (accessed 2 March 2018). 65 ibid. 66 Chiara Palazzo & Peter Foster, ‘Assad Bears Full Responsibility: how the World Reacted to Donald Trump’s Missile Strike on Syria’, The Telegraph, (7 April 2017) <www.telegraph.co.uk/news/2017/04/07/us-air-strike-syria-world-reacted-donald-trumps-decision-intervene/> (accessed 2 March 2018). 67 Ibid. 68 Reuters, ‘Chemical weapons a red line in Syria, France's Macron says’, (29 May 2017), <www.reuters.com/article/us-france-russia-syria-macron/chemical-weapons-a-red-line-in-syria-frances-macron-says-idUSKBN18P1OH> accessed 2 March 2018. 69 Park (n 64). 70 ibid. 71 ibid. 72 ibid. 73 Palazzo & Foster (n 66). 74 ibid. 75 ibid. 76 ibid. 77 Park (note 64). 78 Ministry of Foreign Affairs of the People’s Republic of China, ‘Foreign Ministry Spokesperson Hua Chunying's Regular Press Conference on April 7, 2017’, <www.fmprc.gov.cn/mfa_eng/xwfw_665399/s2510_665401/t1452149.shtml> accessed 2 March 2018. 79 See art 48 (1) (b) in ILC draft articles (n 18). 80 Barcelona Traction (n 50) para 33. 81 In its draft articles on state responsibility (n 18), the ILC leaves the question open, see art 54. In the commentary to art 54, the ILC notes that ‘there appears to be no clearly recognized entitlement of third states to take countermeasures in the collective interest’, see Draft articles on Responsibility of States for Internationally Wrongful Acts, with commentaries, Yearbook of the International Law Commission, 2001, vol II, Part Two, 139, para 6. Christan J Tams concludes a lengthy analysis of both stats practice and governments’ comments on ILC’s work on state responsibility by arguing that ‘present-day international law recognizes a right of all States, irrespective of individual injury, to take countermeasures in response to large-scale or systematic breaches of obligations erga omnes.’ See Tams Christian J Tams, Enforcing Obligations Erga Omnes in International Law (CUP 2005) 250. 82 See, inter alia, the General Assembly’s Declaration on principles of International Law concerning Friendly Relations and Cooperation among States in accordance with the Charter of the United Nations, GA Res 2625, 24 October 1970. 83 See art 25 (1) in the ILC draft articles (n 18). See also ILC’s commentary to the art 25 (n 80) 80 and Gabcikovo-Nagymaros Project, ICJ Reports (1997) 7, para 51. Support for a plea of necessity as a justification for humanitarian interventions can be found in Ole Spiermann, ‘Humanitarian Intervention as a Necessity and the Threat or Use of Jus Cogens’ (2002) 71 Nordic Journal of International Law 543. 84 Henriksen & Schack (n 14) 144–7. 85 art 25 (2) (b) in ILC draft articles (n 18). 86 See also Ian Brownlie, International Law and the Use of Force by States (OUP 1963) 275. 87 In Nicaragua (n 15) para 190, the ICJ quoted the position of the International Law Commission (see below) 88 See the ILC’s commentary to the draft of the Vienna Convention, Report of the International Law Commission, 18th session (1966), International law Commission Yearbook 172, 247. 89 Michael Schmitt & Chris Ford, ‘The Use of Force in Response to Syrian Chemical Attacks: Emergence of a New Norm?, Justsecurity.org, 8. April 2017 <www.justsecurity.org/39805/force-response-syrian-chemical-attacks-emergence-norm/> accessed 2 March 2018. 90 For an overview of the conditions for the formation of customary international law, see the discussion in Anders Henriksen, International Law (OUP 2017) 24–29. 91 The criteria put forward by Denmark are basically identical to the British, see (n 23). 92 See the criteria in Prime Minister's Office, Chemical Weapon Use by Syrian Regime - UK Government Legal Position, 29 August 2013 (n 21). © Oxford University Press 2018; All rights reserved. For permissions, please e-mail: journals.permissions@oup.com This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/about_us/legal/notices) http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Journal of Conflict and Security Law Oxford University Press

Trump’s Missile Strike on Syria and the Legality of Using Force to Deter Chemical Warfare

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Abstract

Abstract The article discusses the legality of the American missile strike on Syria on 6 April 2017, that was initiated in response to the Assad regime’s alleged (repeated) use of chemical weapons in the Syrian civil war. While the academic debate about the legality under international law of the strike has primarily focused on the legality of humanitarian interventions in the traditional sense, the article argues that the strike should instead be discussed as an example of a particular form for humanitarian intervention; one that merely seeks to deter a state from using chemical weapons against civilians. This seems clear from both official US statements about the strike and from the international reactions to the military operation. The article then provides an overview of the strong international norm against chemical warfare and discusses the potential development of—and likely criteria for—a right in international customary law to use force to deter a state from using chemical weapons against civilians. It is in this vital national security interest of the United States to prevent and deter the spread and use of deadly chemical weapons.1 (President Donald J. Trump, 6 April 2017). 1. Introduction On 6 April 2017, American warships launched a series of cruise missiles at an airbase in Syria.2 The strike—that destroyed around 20 planes and killed a number of Syrian soldiers—was launched a few days after a Syrian fighter jet from the air base in question had (allegedly) dropped a chemical bomb in the town of Khan Shaykhun in Idlid Province killing dozens of people, including several children. In a statement from The White House, US President Donald J Trump stated that the American military action was a response to a ‘horrible chemical weapons attack on innocent civilians’ by ‘Syrian dictator Bashar al-Assad’ that ‘choke out the lives of helpless men, women, and children.’3 There were clear parallels between Trump’s decision to order a military strike on Assad in response to the regime’s use of chemical weapons and then-president Barack Obama’s threat of using military force against the Assad-government in 2013 after a chemical attack by Syrian forces in Gouta near the Syrian capital of Damascus.4 A year prior to Obama’s threat, the president had infamously declared that any use of chemical weapons in the Syrian civil war constituted a ‘red line’ the crossing of which would have ‘enormous consequences’.5 Obama never followed-up on his threats of using force against Assad and the crisis in 2013 was instead resolved when the United Nations Security Council—on a sudden Russian initiative—became involved and on 27 September 2013, adopted a resolution demanding that Syria cooperated with the Organization for the Prohibition of Chemical Weapons (OPCW) and destructed all its chemical weapons.6 Two weeks prior to that, Syria had rushed to sign the 1993 Chemical Weapons Convention to which it had not previously been a party.7 When it deposited its instrument of accession to the Convention, the Syrian Government declared that it would ‘comply its stipulations and observe them faithfully and sincerely’.8 Events since the 2013-crisis has shown, however, that the Syrian regime did not fully cooperate with the OPCW and in both 2015 and 2016, the Security Council condemned the continued use of chemical warfare in the Syrian war, including by the Syrian Government.9 The consistent use of chemical weapons in Syria has been confirmed by a range of OPCW fact-finding missions.10 In June 2017, one such mission concluded that chemical weapons had indeed been used in the attack in Khan Shaykhun in April 2017.11 On 26 October 2017, an OPCW—UN Joint Investigative Mechanism (JIM) created by the Security Council to identify those involved in the use of chemical weapons in Syria,12 stated that it was ‘confident’ that the Syrian Government was ‘responsible for the release of sarin at Khan Shaykhun on 4 April 2017’.13 The Trump Administration has not put forward any legal justification for the military operation against Syria but the academic debate about the legality of the operation has primarily been concentrated on the by now well-known arguments for and against the legality of humanitarian intervention without a mandate from the UN Security Council. So when evaluating the American strike, legal experts have for the most part debated if a state like the United States is entitled to use force in a state like Syria in the absence of an authorization from the United Nations Security Council in order to try to bring a halt to an unfolding humanitarian crisis. Here, too, the events surrounding the American strike on Syria resemble the situation in the 2013-crisis where Obama’s threat to use force in Syria ignited a heated debate about the legality of unilateral humanitarian interventions.14 The purpose of the present article is two-fold. First, it will argue that the American strike on Syria does not fit very well with our traditional understanding of what a humanitarian intervention is. Both the political justifications offered by the US Government as well as the international reaction strongly indicate that the military operation should instead be perceived of as having the more limited purpose of seeking to deter the Syrian regime from continuing its use of chemical weapons against civilians in the civil war. Secondly, the article will build upon that conclusion and ask what it would take for a state to be entitled to use non-UN sanctioned military force against another state to deter it from resorting to chemical warfare against civilians. Is such a right on the horizon? What might it look like? The article concludes that although a right to use non-UN sanctioned force to deter chemical warfare against civilian is not yet established, the positive international reaction to the US strike on Syria could indicate that such a right may be in the early stages of creation. The analysis begins in Section 2 with a brief overview of the well-known discussion of a right to humanitarian intervention without a mandate from the Security Council and an explanation of why the American strike on Syria does not fit the traditional category of a humanitarian intervention. Section 3 provides an overview of the strong international norm against chemical warfare before Section 4 discusses the legality of the American strike and the likelihood of the emergence of a right to use force to deter the use of chemical weapons. Section 5 contains a short conclusion. 2. Humanitarian intervention? Any analysis of the legality under international law of using force against another state takes its point of departure in the 1945 Charter of the United Nations. The structure of the Charter is well-known to most readers of this journal. The central provision in the Charter is Article 2 (4) that contains an overall prohibition on the use of force whereby all member states ‘shall refrain in their international relations from the threat or use of force against the territorial integrity or political independence of any state, or in any other manner inconsistent with the Purposes of the United Nations’. According to the ICJ, the prohibition in Article 2(4) is also reflected in customary international law.15 Importantly, Article 2(4) covers all possible uses of force including the use of force for humanitarian purposes.16 The Charter entrusts the Security Council with the primary responsibility for the maintenance of international peace and security and to that end provides the Council with wide-ranging powers, including the competence to authorize the use of force if required to restore or uphold international peace.17 In addition, Article 51 stipulates that states retain their ‘inherent’ right of individual or collective self-defence if an armed attack occurs until the Security Council has taken measures necessary to maintain international peace and security. The Charter system for using force is therefore essentially fairly straightforward. States can only use force against another state if authorized by the Security Council or if compatible with a right to self-defence.18Several attempts has nevertheless been made to argue for the legality of using force in another state for the purposes of putting a halt to widespread atrocities against a local population in the absence of a mandate from the Security Council. While there is no need here to re-enact the lengthy debate about the legality of such unilateral humanitarian interventions,19 it is worth noting that most proponents of a right to humanitarian intervention derive the right from customary international law. Support is primarily found in NATO’s non-UN sanctioned humanitarian intervention in Kosovo in 1999.20 However, a closer look at the events in 1999 reveals that the majority of states that participated in the Kosovo intervention were actually very reluctant to officially argue that their actions were lawful under international law. In fact, most of the states preferred to claim that their intervention was probably unlawful but nevertheless legitimate. To date, only the United Kingdom21, Belgium22 and Denmark23 have officially argued that non-UN-sanctioned use of force for humanitarian purposes can be compatible with international law. The United States is among the states that have yet to claim that a non-UN sanctioned humanitarian intervention can be compatible with international law. So far, Washington seems to prefer the ‘unlawful but legitimate’ position.24 The closest the United States has come to arguing for a right to unilateral humanitarian intervention was an August 2013 statement in which president Obama’s White House Counsel noted that a potential upcoming military operation against Syria without backing from the United Nations in response to Syria’s use of chemical weapons would be ‘justified and legitimate under international law’ even though it would not fit ‘a traditionally recognized legal basis under international law’.25 The American reluctance to go ‘all inn’ in the debate about humanitarian intervention has been criticized by, among others, former legal adviser in the US State Department Harold Hongju Koh. Koh was among those who argued for the legality of non-UN-sanctioned humanitarian intervention in Syria in 2013.26 In 2016, Koh identified a range of criteria that he considers should guide the determination of the legality of humanitarian uses of force not sanctioned by the Security Council.27 In his defense of non-UN-sanctioned humanitarian interventions, Koh links such an alleged right to the doctrine of Responsibility to Protect (R2P).28 That is remarkable because it is pretty clear that the R2P doctrine does not justify using force in the absence of a mandate from the Security Council.29 In fact, the 2005 UN World Summit Outcome Document that Koh refers to in his 2016 article explicitly states that any ‘collective action’ to enforce the doctrine must be taken ‘through the Security Council, in accordance with the Charter, including Chapter VII’.30 Despite the various attempts to argue for a right to use force for humanitarian purposes without a mandate from the UN Security Council, it is hard to find support for the claim that customary international law has progressed to a stage that it would allow such use of force.31 Proponents of a right to unilateral humanitarian intervention tend to ignore the strong non-Western opposition to humanitarian interventions. As noted in the introduction, the United States has not offered any legal justification for the military operation against Syria but the majority of scholars that have voiced their opinion about the legality of the operation appear to consider the strike as an example of a non-UN sanctioned humanitarian intervention. For the most part, therefore, the scholars also find that the strike was incompatible with international law.32 But the present author is not convinced that the American strike on Syria should be considered as a humanitarian intervention—at least not in a conventional sense. While it is true that the US operation was initiated in response to atrocious acts committed by the Syrian regime against the Syrian civilian population, the decision to launch the strike does not appear to be motivated by an overarching desire to put a halt to the war in Syria and thus to stop the suffering of Syrian civilians as such. Rather, statements by the Trump-administration clearly indicate that the strike was motivated by a less ambitious (some might say cynical) attempt to merely stop those parts of the human atrocities that are perpetrated by chemical weapons. In his political justification for the missile strike, President Trump explicitly linked the need to respond to the ‘horrible chemical weapons attack on innocent civilians’ to the ‘vital national security interest of the United States to prevent and deter the spread and use of deadly chemical weapons’. Trump also stated how there ‘can be no dispute that Syria used banned chemical weapons, violated its obligations under the Chemical Weapons Convention, and ignored the urging of the U.N. Security Council’.33 The US National Security Advisor, General McMaster, stated that the strike on Syria was meant to ‘deter the continued use, because there’s been a pattern of the abuse of chemical weapons by the Assad regime and his mass murder attacks against innocent civilians … The objective was to send a very strong political message to Assad.’34 Similar statements came from the American Secretary of Defence, General Mattis, who noted that the purpose of the strike was to ‘deter future use of chemical weapons and to show the United States will not passively stand by while Assad murders innocent people with chemical weapons, which are prohibited by international law and which were declared destroyed.’35 The international reaction to the missile strike also strongly indicates that the operation should be perceived of as an attempt to deter the Assad-regime from continuing its use of chemical weapons in the Syrian civil war and not as a humanitarian intervention in the classic sense. As we shall return to in Section 4, the overwhelmingly positive political reactions to the American use of force were for the most part explicitly tied to Assad’s unlawful use of chemical weapons. Rather than discussing if the American strike on Syria was compatible with a potential right to humanitarian intervention without a Security Council mandate, the legal analysis of the operation should therefore focus on the legality of using non-Council-sanctioned force to deter a state from engaging in chemical warfare. That is the focus of the remainder of the article. 3. The norm against chemical warfare There is a very strong international norm against any use of chemical weapons in armed conflict.36 In his examination of the origins of what he calls the ‘chemical weapons taboo’, Richard Price notes how the objection to chemical warfare originally seemed to be derived from the practical difficulty of controlling the release of chemical substances and the accompanying risk that both combatants and civilians would be exposed to the chemicals. Using chemical weapons was hereby deemed to be incompatible with the fundamental law of war principle of distinction that requires parties to a conflict not to use weapons that cannot distinguish between military and civilian objectives.37 But the norm against chemical warfare also appears to be tied to an ancient ethical objection to using poison as a weapon in war.38 It seems that chemical warfare violates basic norms of ‘civilized’ behaviour regardless of against who the chemical weapons are used.39 In the seminal Tadíc case, the International Criminal Tribunal for the former Yugoslavia (ICTY) referred to chemical weapons as an example of a weapon deemed inherently inhumane.40 The earliest prohibition in international law against chemical warfare is found in a declaration adopted at the 1899 Peace Conference in Haag where the contracting parties agreed to ‘abstain from the use of projectiles the sole object of which is the diffusion of asphyxiating or deleterious gases.’41 Following the widespread use of chemical weapons in the trenches in World War I,42 the 1925 Protocol for the Prohibition of the Use in War of Asphyxiating, Poisonous or Other Gases, and of Bacteriological Methods of Warfare was adopted at a conference in Geneva. The Protocol—that entered into force in 1928—prohibits the use of biological and chemical warfare, and it served as the primary legal instrument for the prohibition of chemical weapons until the adoption on 13 January 1993, of the Convention on the Prohibition of the Development, Production, Stockpiling and Use of Chemical Weapons and their Destruction. As its name reveals, this Chemical Weapons Conventions (CWC) prohibits not only the use of chemical weapons in times of armed conflict but also their development, storing, as well as military preparations for chemical warfare.43 The CWC obliges states to destroy chemical weapons they may be in possession of, to dismantle their facilities for producing chemical weapons44 and to comply with a verification and inspection regime.45 The Convention created the Organization for the Prohibition of Chemical Weapons (OPCW) in The Hague, the Netherlands, where all state parties meet in annual conferences to discuss matters and issues that fall within the scope of the Convention. The OPCW is headed by an Executive Council consisting of 41 members. By November 2017, the CWC—that entered into force in 1997—had 192 parties.46 Egypt, North Korea and South Sudan have neither signed not ratified the convention. Israel has signed the Convention but not (yet) ratified it. It is widely held that the prohibition against using chemical weapons reflects customary international law in both international and non-international armed conflicts.47 As already noted, in Tadíc, the ICTY referred to chemical weapons as an example of a weapon that is considered inhumane in all types of armed conflict.48 The use of chemical weapons in an international armed conflict is also listed in the 1999 Rome Statute as a war crime within the jurisdiction of the International Criminal Court (ICC).49 The obligation not to use chemical weapons would also appear to constitute an obligation erga omnes that is owed to the ‘the international community as a whole’.50 The strong norm against chemical warfare is also reflected in resolutions adopted by the UN Security Council. On 28 April 2004, the Council adopted Resolution 1540 concerning non-proliferation of weapons of mass destruction. The resolution begins by affirming ‘that the proliferation of … chemical … weapons, as well as their means of delivery, constitutes a threat to international peace and security’. The Resolution was adopted pursuant to Chapter VII of the Charter and it contains a range of obligations aimed at preventing the spread of such weapons. It also created an ad hoc committee—the ‘1540 Committee’—for purposes of monitoring the implementation of the resolution. Despite the long-existing prohibition on using chemical weapons in armed conflict there are numerous examples of (prohibited) chemical warfare.51 Up until the chemical attacks in the civil war in Syria, the best-known recent example is Iraq’s campaign of chemical warfare in its war against Iran (1980–1988) and its extensive use of chemical gas against its own Kurdish population in the so-called ‘Anfal Campaign’ (1986–1989) in the North of Iraq.52 In one attack alone, in the town of Halabja, chemical gases killed an estimated 5000 Kurdish civilians. Iraq’s use of chemical weapons against the Kurds were condemned by many states53 and in June 2007, the ‘mastermind’ of the chemical attacks against the Kurds—Ali Hassan Al-Majid (also known as ‘Chemical Ali’)—was found guilty of genocide and sentenced to death by an Iraqi court.54 In 2007, insurgents and operatives of Al Qaida in Iraq (AQI) attempted to release chlorine gases in Improvised Explosive Devices (IEDs) in truck bombs in the war in Iraq.55 Terrorist organizations have also used chemical substances outside armed conflict. In 1994 and 1995, a Japanese sect (Aum Shinriko) released Sarin nerve gas in the Japanese cities of Matsumoto and Tokyo, killing 13 people.56 In addition, from its sanctuary in Afghanistan, Al Qaida actively sought to develop chemical weapons for potential use in terrorist attacks in the late 1990s.57 As mentioned in the introduction, the Security Council became involved in the crisis following the 2013 Gouta-attack in Syria when US President Obama refrained from moving ahead with the threatened military operation against Assad and instead sought to find a diplomatic solution to the crisis. In Resolution 2118, the Council on 27 September 2013 responded to the Gouta-attack by condemning the use of chemical weapons in Syria and reaffirmed ‘that the proliferation of chemical weapons, as well as their means of delivery, constitutes a threat to international peace and security’ as well as ‘a serious violation of international law’. The Council also stressed how ‘those responsible for any use of chemical weapons must be held accountable’ and it welcomed the establishment by the UN Secretary-General of a Mission to Investigate Allegations of the Use of Chemical Weapons in Syria. On 14 September 2013, Syria had signed the CWC and promised to comply with the provisions of the Convention even though it would only become formally binding on that state 30 days later.58 In Resolution 2235, the Security Council on August 7, 2015, noted ‘with outrage that civilians continue to be killed and injured by toxic chemicals as weapons’ in Syria and stressed again ‘that those individuals responsible for any use of chemical weapons must be held accountable’. The Council established an OPCW–UN Joint Investigative Mechanism to identify those who are involved in the use of chemical weapons in Syria where a fact-finding mission by the OPCW has determined that chemical weapons has been used.59 Since its creation, the Mechanism has published seven reports that have concluded that both the Syrian Armed Forces as well as the Islamic State in Iraq and Levant (ISIL) had used chemical weapons in the war in Syria.60 As noted in the introduction, in October 2017, the Mechanism concluded that it was the Syrian Government that was behind the chemical attack in Khan Shaykhun in April 2017.61 The Council extended the mandate of the Mechanism for one year in November 201662, but in October 2017 a Russian veto prevented the Security Council from reaching agreement on a further extension.63 The international reaction to the American missile strike on Syria in April 2017 illustrates how strong the norm against chemical warfare is. Thus, with the exception of Russia64 and Iran,65 states have generally offered solid political support for President Trump’s decision to use military force against the Assad-regime in response to its chemical attacks in the civil war. Shortly after the strike, a spokesperson from the British Government stated that the United Kingdom ‘fully supports the US action, which we believe was an appropriate response to the barbaric chemical weapons attack launched by the Syrian regime, and is intended to deter further attacks’.66 In a joint statement, the French President and the German Chancellor stated that ‘President Assad alone carries responsibility for these developments’ in light of his ‘repeated use of chemical weapons and his crimes against his own people’.67 On 29 May 2017, in response to a question about the war in Syria, French President Emmanuel Macron (then newly elected) also stated that any ‘use of chemical weapons would results in reprisals and an immediate riposte, at least where France is concerned’.68 Immediately after the strike, the President of the European Council, Donald Tusk, tweeted that the operation ‘show much needed resolve against barbaric chemical attacks’.69 NATO’s Secretary-General Jens Stoltenberg noted how ‘NATO has consistently condemned Syria’s continued use of chemical weapons as a clear breach of international norms and agreements’.70 Similar political support coupled with condemnation of Assad’s use of chemical weapons came Spain,71 Italy,72 Australia,73 Israel,74 Japan,75 Saudi Arabia,76 Jordan and Turkey.77 Even China offered its political support to the missile strike without noting that the strike seems hard to reconcile with the UN Charter.78 4. A right to use force to deter chemical warfare against civilians? At the outset it is worth noting that from the perspective of international law, the American strike on Syria in April 2017 can be approached from different angles. Thus, before turning to the discussion of a potential right to use force to deter chemical weapons in customary international law, it is necessary to briefly touch upon two other possible legal justifications for the American strike. The first relates to the issue of countermeasures. The American strike could be perceived of as a response to Syria’s unlawful use of prohibited weapons and thus its violation of international law. The United States was not injured by Syria’s unlawful use of chemical weapons but a non-injured state may be entitled to invoke the responsibility of another state ‘if the obligation breached is owed to the international community as a whole’.79 In Barcelona Traction, the ICJ famously stated that a state may have certain obligations not just to another state but towards ‘the international community as a whole’ and that all states have a legal interest in the protection of such rights.80 As noted in the previous section, Syria’s obligation not to use chemical weapons in armed conflict could very well be an obligation erga omnes that all states, including the United States, has an interest in protecting. One of the ways whereby a state may respond to another state’s internationally wrongful acts is by taking countermeasures in order to bring the wrongful acts to a halt. It is not at present clear if—and if so, how—a non-injured state may resort to countermeasures in response to a breach of international law.81 What is certain, however, is that armed countermeasures are prohibited.82 The American strike on Syria cannot therefore possibly be justified as a lawful countermeasure. A second alternative justification is a plea of necessity. As a concept under international law, necessity relates to those rare cases where the only way for a state to safeguard an essential interest threatened by a grave and imminent peril is, for the time being, not to perform some other international obligation of lesser weight or urgency.83 However, as discussed at greater length elsewhere,84 necessity does not appear to a valid defence to justify violations of the prohibition on the use of force in Article 2(4) of the UN Charter. Most importantly, necessity is unavailable if the international obligation in question ‘excludes the possibility of invoking necessity’.85 While the Charter does not explicitly mention necessity it seems logical to conclude that the Charter is the exclusive source on the international legal regulation of interstate force in the sense that it rules out the invocation of necessity.86 Thus, aside from the powers of the Security Council, the right to self-defence is the only legal defence to a violation of the prohibition on the use of force under international law. It should also be noted that necessity cannot be invoked to justify violating a rule of a jus cogens character. Although one could certainly discuss if the entire prohibition on the use of force in the UN Charter is really of a jus cogens nature, it does seem to be the position by the ICJ87 and the International law Commission.88 This, then, brings us to the status in customary international law. Professor Michael N Schmitt and Lt Col Chris Ford have argued that the American strike on Syria could pave the way for changes to the international regulation of the use force. On 8 April 2017, they noted that we may be: witnessing … the slow and rather painful birth of a nascent right in customary international law allowing States to act forcefully to put an end to the use of particularly repugnant weaponry against a civilian population, or perhaps even one countenancing forceful State responses to other egregious forms of terrorizing and massacring civilian populations in other countries.89 The emergence of a right in customary international law to use force to deter the use of chemical weapons against civilians requires the establishment of a general practice among states that is accepted by those states as legally relevant (opinio juris).90 At present, state practice is far too scarce to lend much support to the conclusion that international law should have changed sufficiently to accommodate the kind of use resorted to by the United States. Thus, despite the positive political reactions to the American strike on Syria, it is clear that the missile strike on Syria was incompatible with international law. This does not preclude, of course, that Schmitt and Ford may not be correct in noting that the law could be gradually moving towards the creation of a right in customary international law to use force to deter chemical warfare. What would the contours of a potential right to use force to deter chemical warfare look like? In practice, of course, the decisive factor will be subsequent state practice as well as the international reactions thereto. But a sensible place to start would be to re-examine the criteria for (alleged) lawful non-UN sanctioned humanitarian intervention that have been put forward by the British and Danish Government. According to the UK and Denmark,91 using force for humanitarian purposes will be compatible with international law if three conditions are fulfilled: (i) ‘there is convincing evidence, generally accepted by the international community as a whole, of extreme humanitarian distress on a large scale, requiring immediate and urgent relief’; (ii) ‘it must be objectively clear that there is no practicable alternative to the use of force if lives are to be saved’; and (iii) ‘the proposed use of force must be necessary and proportionate to the aim of relief of humanitarian need and must be strictly limited in time and scope to this aim’.92 If one were to build on these criteria, the relevant factors for determining the potential future legality of using force to deter a state from using chemical weapons against civilians could look like the following. First, the use of force must be a response to convincing evidence that a state has used chemical weapons against civilians in an armed conflict. One could argue, of course, that a potential right to use force to deter chemical warfare ought to be relevant to all uses of chemical weapons and not only to those instances where chemical weapons has been used against civilians/non-combatants. After all, the legal ban on chemical weapons covers all use of such weapons in armed conflict. Schmitt and Ford appear to limit a potential right to use force to chemical warfare against civilians. This seems sensible because the international condemnation of the chemical attacks in Syria has so far focused on the civilian casualties of using such weaponry. In addition, since a potential right to use force to deter a state from using chemical weapons would be an exception to the overall ban on the use of force in Article 2(4) such an exception should be construed as narrow as possible. This also speaks in favour of limiting a potential emerging customary right to those instances where chemical weapons are used in a non-international armed conflict, such as the conflict in Syria. Secondly, it must be objectively clear that there is no realistic alternative to the use of force if the chemical warfare is to be brought to a halt. Using force without a mandate from the Security Council must always be last resort and any realistic non-forcible avenues for pressuring a state to halt its use of chemical weapons must have been exhausted. To be perceived as politically legitimate, a decision to use force should be supported by as many states as possible, preferably by a regional organization. In that regard it is worth noting that the Trump Administration did not appear to have tried to build a broad international coalition behind its April 6 decision to launch a missile strike against the Assad regime. Washington did not seek, for instance, to involve NATO before they resorted to using force against Syria. The third and final condition is that the use of force is proportionate to the aim of deterring the state that has used chemical weapons from continuing its use of such weapons and strictly limited in time and scope to this aim. This requirement of proportionality will in most cases probably demand that there are indications that continuing uses of chemical weapons are likely. When compared to a less clearly defined and broader right to humanitarian intervention in the traditional sense, a limited right to use force to deter a state from continuing to use chemical weapons against civilians would be fairly clearly demarcated and thus, one would hope, not as prone to potential abuse as the alleged—broader—right to humanitarian intervention as such. 5. Conclusion The American missile strike on Syria was not a humanitarian intervention in the classic sense but a use of force that sought to deter Syria from continuing its chemical warfare against civilians in the civil war in Syria. The American strike was incompatible with international law. It is too early to tell is such an instance of force may one day become lawful under customary international law but the positive political reaction to the strike illustrates that the norm against the use of chemical warfare is very strong. Footnotes 1 D Trump, ‘Statement by President Trump on Syria’ (6 April 2017) <www.whitehouse.gov/the-press-office/2017/04/06/statement-president-trump-syria> accessed 30 November 2017. 2 Michael R Gordon, Helene Cooper and Michael D Shear, ‘Dozens of U.S. Missiles Hit Air Base in Syria’, New York Times (New York, 6 April 2017) <www.nytimes.com/2017/04/06/world/middleeast/us-said-to-weigh-military-responses-to-syrian-chemical-attack.html?_r=0> accessed 2 March 2018. 3 See (n 1). 4 For more, see United Nations Mission to Investigate Allegations of the Use of Chemical Weapons in the Syrian Arab Republic, Report on the Alleged Use of Chemical Weapons in the Ghouta Area of Damascus on 21 August 2013, 16 September 2013, A/67/997-S/2013/553. For a discussion of some of the international law implications of the Syrian use of chemical weapons in 2013, see also Mika Hayashi, ‘Reacting to the Use of Chemical Weapons: Options for Third States’ (2014) 1(1) JUFIL 80–121. 5 Mark Landler, ‘Obama Threatens Force Against Syria’, New York Times (20 August 2012) <www.nytimes.com/2012/08/21/world/middleeast/obama-threatens-force-against-syria.html> accessed 2 March 2018. 6 UNSC Res 2118 (27 September 2013), para 4, 6 & 7. 7 The Convention entered into force for Syria on 14 October 2013, see <www.opcw.org/about-opcw/member-states/member-states-by-region/asia/member-state-syria/> accessed 2 March 2018. 8 See OPCW, Executive Council, Decision Destruction of Syrian Chemical Weapons, EC-M-33/DEC.1, 27 September 2013, available at <www.opcw.org/fileadmin/OPCW/EC/M-33/ecm33dec01_e_.pdf> (accessed 2 March 2018). 9 UNSC Res 2235 (7 August 7 2015) and UNSC Res 2319 (17 November 2016). 10 For an overview of OPCW fact-finding missions in Syria, see www.opcw.org/special-sections/syria/fact-finding-mission-reports/> accessed 2 March 2018. 11 Report of the OPCW Fact-Finding Mission in Syria Regarding an Alleged Incident in Khan Shaykhun, Syrian Arab republic April 2017, S/1510/217, 29 June 2017. 12 Res 2235 (n 9) para 5. 13 Seventh Report of the Organization for the Prohibition of Chemical Weapons-United Nations Joint Investigative Mechanism, 10. See S/2017/904, 26 October 2017. 14 For a discussion, see A Henriksen and M Schack, ‘The Crisis in Syria and Humanitarian Intervention’ (2014) 1(1) JUFIL 122–47. 15 Military and Paramilitary Activities in and against Nicaragua (Nicaragua v United States of America). Merits, Judgment ICJ Reports 1986, 14, paras 188–90. 16 Y Dinstein, War, Aggression and Self-Defence (5th edn, Cambridge University Press) 90; I Brownlie, International Law and the Use of Force by States (OUP 1963) 265–8; T Franck, Recourse to Force: State Action Against Threats and Armed Attacks (CUP 2002) 12; A Randelzhofer, ‘Article 2(4)’ in B Simma (ed) The Charter of the United Nations: A Commentary (2nd edn, OUP 2002) 123. 17 See art 42 of the UN Charter. 18 Please note that valid consent by a territorial state to the use of force on its territory by another state precludes the wrongfulness of the latter state’s acts as long as these remains within the limits of that consent, sea art 20 of the International Law Commission’s 2001 draft articles on Responsibility of States for Internationally Wrongful Acts, see GA Res 56/83 of 12 December 2001, corrected by document A/56/49(Vol I)/Corr 4. 19 For a comprehensive debate, see Henriksen & Schack (n 14). 20 ibid, 138–42. 21 The United Kingdom was the first state to officially argue that an intervention like the one in Kosovo could be legal as an ‘extraordinary measure to prevent an overwhelming humanitarian catastrophe’, see S/PV.3988, 24 March, 12. The British repeated its claim in 2013 in connection with the prospects of a potential US-led military action against Syria in response to the August 2013 Gouta chemical weapons attack, see Prime Minister’s Office, Chemical Weapon Use by Syrian Regime - UK Government Legal Position (29 August 2013) <www.gov.uk/government/publications/chemical-weapon-use-by-syrian-regime-uk-government-legal-position/chemical-weapon-use-by-syrian-regime-uk-government-legal-position-html-version> accessed 2 March 2018. 22 Belgium argued for the international legality of the 1999 intervention in the course of proceedings before the International Court of Justice (ICJ) in a case brought against NATO members by the former Yugoslavia, see Legality of Use of Force (Serbia and Montenegro v Belgium), Oral Proceedings, Public sitting, 10 May 1999, 12. 23 In 2013, Denmark supported the British legal position that humanitarian intervention without an authorization from the Security Council could be lawful, see ‘Overordnede principielle overvejelser om det folkeretlige grundlag for en evt. militær operation i Syrien’, in Udenrigspolitisk Nævn, bilag 298, alm del, 2012–2013. See also Danish Ministry of Defence, Militærmanual om folkeret for danske væbnede styrker i internationale militære operationer (September 2016) 16. 24 The American justification for the intervention in Kosovo is available in Michael J Matheson, ‘Justification for the NATO Air Campaign in Kosovo, (2000) 94 ASILP 301. For an overview of the American position vis-à-vis humanitarian intervention, see also Harold Hongju Koh ‘Address: The War Powers and Humanitarian Intervention’ (2016) 53 Houston Law Review 971–1033. 25 See Charlie Savage, ‘Obama Tests Limits of Power in Syrian Conflict’ New York Times (8 September 2013) <www.nytimes.com/2013/09/09/world/middleeast/obama-tests-limits-of-power-in-syrian-conflict.html> accessed 2 March 2018. 26 Harold Hongju Koh, ‘Syria and the Law of Humanitarian Intervention (Part II: International Law and the Way Forward)’ (Just Security, 2 October 2013) <www.ejiltalk.org/syria-and-the-law-of-humanitarian-intervention-part-ii-international-law-and-the-way-forward/> accessed 30 November 2017. 27 Koh (2016) (n 24) 1011. 28 ibid 976, 1004–1010 and 1032. 29 See also Henriksen & Schack (n 14) 128–33. 30 GA Res 60/1, World Summit Outcome Document, 24 October 2005, s 139. See also the statement by the UN Secretary-General in UN Document, A/63/677, 2009, para 3. 31 See the discussion and references in Henriksen & Schack (n 14) 128–33 32 For an overview of academic positions, see Ryan Goodman, ‘What Do Top Legal Experts Say About the Syria Strikes?’ (Just Security, 7. April 2017) <www.justsecurity.org/39712/top-legal-experts-syria-strikes/> accessed 30 November 2017; John Bellinger, ‘What was the Legal Basis for the U.S. Air Strikes Against Syria?’ (Lawfare, 6 April 2017) <www.lawfareblog.com/what-was-legal-basis-us-air-strikes-against-syria> accessed 30 November 2017; Marty Lederman, ‘Why the Strikes Against Syria Probably Violate the U.N. Charter and (therefore) the U.S. Constitution’ (Lawfare, 6 April 2017) <www.justsecurity.org/39674/syrian-strikes-violate-u-n-charter-constitution/> accessed 30 November 2017; Ashley Deeks, ‘How Does the Syria Situation Stack up to the “Factors” that Justified Intervention in Kosovo?’ (Lawfare, 7 April 2017) <www.lawfareblog.com/how-does-syria-situation-stack-thefactors-justified-intervention-kosovo> accessed 30 November 2017. For a more positive assessment, see Harold Hongju Koh, ‘Not Illegal: But Now the Hard Part Begins’, (Just Security, 7 April 2017) <www.justsecurity.org/39695/illegal-hard-part-begins/> 30 November 2017. 33 See (n 1). 34 ‘Exclusive: General H.R. McMaster on decision to strike Syria’, Fox News, 9 April 2017 <www.foxnews.com/transcript/2017/04/09/exclusive-general-h-r-mcmaster-on-decision-to-strike-syria.html> acceessed 2 March 2018. 35 Statement by Secretary of Defense Jim Mattis on the U.S. Military Response to the Syrian Government’s Use of Chemical Weapons, 10 April 2017 <www.defense.gov/News/News-Releases/News-Release-View/Article/1146758/statement-by-secretary-of-defense-jim-mattis-on-the-us-military-response-to-the/> accessed 2 March 2018. 36 Richard Price, ‘A Genealogy of the Chemical Weapons Taboo’ (1995) 49 International Organizations, Winter 73–103. Chemical warfare agents consist of manmade toxic chemicals like chlorine, phosgene and sarin nerve gas. For an overview of the international regulation of chemical weapons, see William H Boothby, Weapons and the Law of Armed Conflict (OUP 2009) 129–39. For an analysis of the threat of chemical weapons, see Jonathan B Tucker, ‘The Future of Chemical Weapons’ (2009/2010) The New Atlantis, Fall/ Winter 3–29. [AQ] 37 Price (n 36) 82–3. 38 See also the 1874 Brussel Declaration that sought to outlaw the use of poison or poisoned weapons and the 1880 Manual on The Laws of War on Land, Oxford. 39 The prohibition against using chemical weapons was not always deemed applicable in wars against ‘uncivilized’ nations or peoples, see the references in Boothby (n 36) 10. 40 Prosecutor v Dusko Tadic, Decision on the Defence Motion for Interlocutory Appeal on Jurisdiction, IT-94-1 (2 October 1995), paras 120–24. 41 Declaration (IV, 2) concerning Asphyxiating Gases. The Hague, 29 July 1899. 42 Germany was the first state to use chemical weapons in World War One (at Ypres in April 1915) and by the end of the war an estimated 90,000 people has been killed by toxic agents, see Tucker (n 36) 4. 43 CWC art I. 44 Ibid, art I (2–4). 45 Ibid, art IV. 46 OPWC, Status of Participation in the Chemical Weapons Convention as at 17 October 2015 <www.opcw.org/about-opcw/member-states/> accessed 2 March 2018. 47 Jean-Marie Henckaerts & Louise Doswald-Beck, Customary International Humanitarian law: Volume I: Rules, (CUP 2005), see Rule 74. See also Boothby (n 36) 137–38 and Sandesh Sivakumaran, The Law of Non-International Armed Conflict (OUP 2012) 394. 48 Tadic (n 40) 49 Rome Statute art 82(b) (xviii). 50 Barcelona Traction, Light and Power Company, Limited, Judgment, ICJ Reports 1970, 3, para 33. The ICJ has states that certain obligations under international humanitarian law may be obligations erga omnes, see Legal Consequences of the Construction of a Wall in the Occupied Palestinian Territory, Advisory Opinion, ICJ, Reports 2004, 136, para 155–7. 51 See the short overview in John Kierulf, Disarmament (DJØF Publishing 2017) 135–37. 52 For an elaborate and convincing account of ‘Anfal’, see Human Rights Watch, Genocide in Iraq, The Anfal Campaign Against the Kurds (July 1993) <www.hrw.org/reports/1993/iraqanfal/> accessed 2 March 2018. 53 See the references cited in Tadíc (n 40). 54 CNN, ‘Chemical Ali’ sentenced to hang (14 June 2007) <http://edition.cnn.com/2007/WORLD/meast/06/24/iraq.ali/> accessed 2 March 2018. 55 Tucker (n 36) 14. 56 Kierulf (n 51) 136. 57 Tucker (n 36) 23–24. 58 See the reference in UNSC Res 2118 (n 6). 59 See resolution 2235 (n 8), para 5. 60 See, inter alia, Third Report of the Organization for the Prohibition of Chemical Weapons-United Nations Joint Investigative Mechanism, S/2016/738/Rev.1, 24 August 2016 and Seventh Report of the Organization for the Prohibition of Chemical Weapons-United Nations Joint Investigative Mechanism, S/2017/904, 26 October 2017. 61 See (n 13). 62 Res 2319 (n 9). 63 UN News Centre, ‘Security Council Fails to Extend Mandate of Panel Investigating Use of Chemical Weapons in Syria’, 24 October 2017 <https://news.un.org/en/story/2017/10/569212-security-council-fails-extend-mandate-panel-investigating-use-chemical-weapons> accessed 2 March 2018. 64 Madison Park, ‘Who's with the US on Syria Strike and who isn't’ CNN (9 April 2017) <http://edition.cnn.com/2017/04/07/world/syria-us-strike-world-reaction/> (accessed 2 March 2018). 65 ibid. 66 Chiara Palazzo & Peter Foster, ‘Assad Bears Full Responsibility: how the World Reacted to Donald Trump’s Missile Strike on Syria’, The Telegraph, (7 April 2017) <www.telegraph.co.uk/news/2017/04/07/us-air-strike-syria-world-reacted-donald-trumps-decision-intervene/> (accessed 2 March 2018). 67 Ibid. 68 Reuters, ‘Chemical weapons a red line in Syria, France's Macron says’, (29 May 2017), <www.reuters.com/article/us-france-russia-syria-macron/chemical-weapons-a-red-line-in-syria-frances-macron-says-idUSKBN18P1OH> accessed 2 March 2018. 69 Park (n 64). 70 ibid. 71 ibid. 72 ibid. 73 Palazzo & Foster (n 66). 74 ibid. 75 ibid. 76 ibid. 77 Park (note 64). 78 Ministry of Foreign Affairs of the People’s Republic of China, ‘Foreign Ministry Spokesperson Hua Chunying's Regular Press Conference on April 7, 2017’, <www.fmprc.gov.cn/mfa_eng/xwfw_665399/s2510_665401/t1452149.shtml> accessed 2 March 2018. 79 See art 48 (1) (b) in ILC draft articles (n 18). 80 Barcelona Traction (n 50) para 33. 81 In its draft articles on state responsibility (n 18), the ILC leaves the question open, see art 54. In the commentary to art 54, the ILC notes that ‘there appears to be no clearly recognized entitlement of third states to take countermeasures in the collective interest’, see Draft articles on Responsibility of States for Internationally Wrongful Acts, with commentaries, Yearbook of the International Law Commission, 2001, vol II, Part Two, 139, para 6. Christan J Tams concludes a lengthy analysis of both stats practice and governments’ comments on ILC’s work on state responsibility by arguing that ‘present-day international law recognizes a right of all States, irrespective of individual injury, to take countermeasures in response to large-scale or systematic breaches of obligations erga omnes.’ See Tams Christian J Tams, Enforcing Obligations Erga Omnes in International Law (CUP 2005) 250. 82 See, inter alia, the General Assembly’s Declaration on principles of International Law concerning Friendly Relations and Cooperation among States in accordance with the Charter of the United Nations, GA Res 2625, 24 October 1970. 83 See art 25 (1) in the ILC draft articles (n 18). See also ILC’s commentary to the art 25 (n 80) 80 and Gabcikovo-Nagymaros Project, ICJ Reports (1997) 7, para 51. Support for a plea of necessity as a justification for humanitarian interventions can be found in Ole Spiermann, ‘Humanitarian Intervention as a Necessity and the Threat or Use of Jus Cogens’ (2002) 71 Nordic Journal of International Law 543. 84 Henriksen & Schack (n 14) 144–7. 85 art 25 (2) (b) in ILC draft articles (n 18). 86 See also Ian Brownlie, International Law and the Use of Force by States (OUP 1963) 275. 87 In Nicaragua (n 15) para 190, the ICJ quoted the position of the International Law Commission (see below) 88 See the ILC’s commentary to the draft of the Vienna Convention, Report of the International Law Commission, 18th session (1966), International law Commission Yearbook 172, 247. 89 Michael Schmitt & Chris Ford, ‘The Use of Force in Response to Syrian Chemical Attacks: Emergence of a New Norm?, Justsecurity.org, 8. April 2017 <www.justsecurity.org/39805/force-response-syrian-chemical-attacks-emergence-norm/> accessed 2 March 2018. 90 For an overview of the conditions for the formation of customary international law, see the discussion in Anders Henriksen, International Law (OUP 2017) 24–29. 91 The criteria put forward by Denmark are basically identical to the British, see (n 23). 92 See the criteria in Prime Minister's Office, Chemical Weapon Use by Syrian Regime - UK Government Legal Position, 29 August 2013 (n 21). © Oxford University Press 2018; All rights reserved. For permissions, please e-mail: journals.permissions@oup.com This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/about_us/legal/notices)

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Published: Mar 16, 2018

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