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Does Use of Chemical Weapons Justify Intervention in Syria?

Does Use of Chemical Weapons Justify Intervention in Syria?


Over the last few days, various media outlets have reported that the US, UK and other countries believe that the Syrian government has used chemical weapons in the Syrian conflict (see BBC report). Apparently, there is not yet conclusive evidence of this and the US and others are investigating the matter. However, US President Obama has stated that use of chemical weapons would be a “game changer.”



“Horrific as it is when mortars are being fired on civilians and people are being indiscriminately killed, to use potential weapons of mass destruction on civilian populations crosses another line with respect to international norms and international law.


“All of us, not just the United States, but around the world, have to recognise how we cannot stand by and permit the systematic use of weapons like chemical weapons on civilian populations,” he said


So, the question is whether, as a matter of international law, the use of chemical weapons would justify intervention in Syria. Military intervention in Syria either directly (by the armed forces of other States) or indirectly (by providing arms to the Syrian opposition) would, in principle, be contrary to Article 2(4) of the United Nations Charter. The issue is whether there are any arguments that may be used to get round the prohibition of the use of force in that provision. In previous posts I have considered the legality of arming the opposition in Syria  (and also here) and after examining the different arguments that may be used, concluded that none of them has a strong basis in international law. It does not seem to me that the use of chemical weapons changes the position as a matter of international law.


The main argument that could be used to justify intervention if it is established that chemical weapons have been used would be humanitarian intervention. However, to my knowledge, the United States has never relied on this as a legal basis for intervention (I would be grateful for clarification if I am wrong on this). Most importantly, most States reject the view that international law permits States to use force in other States for humanitarian reasons. Perhaps views on this are changing – for example it is not clear whether French and Arab support for arming the Syrian opposition are based on a humanitarian intervention typer argument. Perhaps a use of chemical weapons might change the views of others such that we see the law changing. However, I doubt that there will be enough of a shift in State practice and opinio juris arising out of the conflict in Syria for us to say that humanitarian intervention can really be regarded as lawful.


Ashley Deeks in a typically excellent post on Lawfare  back in December (and another post of yesterday) addressed possible legal arguments that might be deployed with regard to a response to a use of chemical weapons. She started with an interesting argument based not on humanitarian intervention but on collective self-defence:



“The USG [United States’ Government] might believe that a Syrian use of chemical weapons is likely to affect neighboring (and friendly) states such as Turkey and Jordan. Depending on where Assad used the weapons and what the atmospheric conditions were, it might be the case that the chemical weapons could drift across national boundaries – and be deemed an armed attack on that neighboring state. This might set up a theory along the lines of “anticipatory collective self-defense,” particularly where the relevant neighboring states already have asked the United States to intervene on their behalf. This is, as far as I’m aware, an untested theory.”


I think that this might well be a plausible argument, though the fact pattern that would justify it is rather specific and perhaps rather limited. I pause to note that Obama’s language seems much  more expansive than this. It is language much closer to the humanitarian intervention justification. But perhaps US lawyers would in the end rely on more limited justifications were force actually to be used.


One possible obstacle that might arise with regard to the collective (or even individual) self defence argument – even on this specific fact pattern – is whether the drifting of chemical weapons across the border should be regarded as constituting an armed attack, when it happens unintentionally. In the Oil Platforms Case, the ICJ appeared to suggest that for a use of force by one State which affects another to consitute an armed attack on the latter, the former State must have intended to target the latter State. It stated



“There is no evidence that the minelaying alleged to have been carried out by the [Iranian vessel] Iran Ajr, at a time when Iran was at war with Iraq, was aimed specifically at the United States; and similarly it has not been established that the mine struck by the [US vessel] Bridgeton was laid with the specific intention of harming that ship, or other United States vessels. Even taken cumulatively, and reserving, as already noted, the question of Iranian responsibility, these incidents do not seem to the Court to constitute an armed attack on the United States, of the kind that the Court, in the case concerning Military and Paramilitary Activities in and against Nicaragua, qualified as a “most grave” form of the use of force ” [Para. 64, emphasis added]


In my view, the ICJ was wrong to consider the question of intention as going to whether there is an armed attack or not.  Th. is point should go to the criterion of necessity (and also by extension proportionality)The intention of the “attacking” State should be relevant to whether or not the “victim” has the right to respond in self-defence but this should not be because there is a lack of an armed attack – when plainly arms have been used against that State. The question is whether the lack of intention to attack means that it is not necessary to respond in self-defence. Where there is a genuine mistake then perhaps it would be unnecessary to respond with force. An alternative (diplomatic) solution might be available and thus required by the law. But perhaps lack of intention does not mean that an alternative solution is available (eg the mistaken State refuses to take any steps to correct error and continues to act in ways in which the mistake continues to be repeated or is likely to be repeated). In this case, self defence ought to be available as force is necessary to prevent further uses of force affecting the State. On this analysis, Oil Platforms ought not to stand in the way of Ashley Deek’s argument.


However, even on Ashley’s self-defence argment, the question would be what sort of intervention would be lawful. Would this sort of cross border /self defence type justify force to remove the Assad government in Syria. Arguably, the proportionality criterian suggests that force should only be used that is necessary to prevent the cross border spread of chemicals. Surely this would not allow direct or indirect uses of force to remove Assad! Or would it? It may be argued that if this is a government prepared to use chemical weapons, the only way to stop it from continuing to do so is to remove it. We would be in terrain very similar to arguments  made with regard to Iraq in 2002/03 and of course in Libya in 2011 where it was argued that removal of Gaddafi was necessary to protect civilians. We considered this matter quite extensively back in 2011 (see here and herehere) and it would not be surprising to see arguments based on necessity to prevent use of chemical weapons being used to justify removal of a government.



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