Yesterday President Trump apparently aborted a US strike against Iran, in response to Iran’s destruction of an unmanned US surveillance drone. US and Iranian accounts continue to differ on whether the drone was shot down in Iranian airspace or in international airspace. Ashley Deeks and Scott Anderson have helpfully analyzed the international legal framework applicable to any US strike in response to the destruction of the drone over on Lawfare, to which I have little to add in principle. In particular, they’ve explained the more expansive and the more restrictive theories of self-defence on which the legality of a US strike would hinge (see also Ashley’s previous post here).
But, President Trump has tweeted in the past hour, as he does, and his tweets effectively (if inadvertently) admit the illegality of the aborted US strike under any conceivable theory of self-defence, no matter how expansive:
….proportionate to shooting down an unmanned drone. I am in no hurry, our Military is rebuilt, new, and ready to go, by far the best in the world. Sanctions are biting & more added last night. Iran can NEVER have Nuclear Weapons, not against the USA, and not against the WORLD!
— Donald J. Trump (@realDonaldTrump) June 21, 2019
Note, first, how President Trump describes the aborted US strike as being meant ‘to retaliate’ against Iran for the destruction of the drone. But it is black letter jus ad bellum that the purpose of self-defence can only be to stop an ongoing attack, or (possibly) to prevent imminent future attacks. It cannot, however, simply be to retaliate against an attack committed in the past. Thus, even if US historically expansive views on the right to self-defence were to be accepted in their totality, and even we were to accept that the US drone was in international airspace when it was shot down and that this was an armed attack by Iran against the US in the sense of Article 51 of the UN Charter, the US head of state has just admitted to the world that the strike he authorized, and then rescinded, was retaliatory and not defensive in nature.
Similarly, he expressly admitted that the attack would have been disproportionate, as 150 lives would likely have been lost for one destroyed unmanned drone. And as we all know, proportionality is a key requirement of the customary law of self-defence. Thankfully, President Trump ultimately decided to abort the strikes, and therefore no violation of Article 2(4) of the UN Charter took place. Hopefully any conflict between the US and Iran will be avoided. But that said, it is also clear from what the US President tweeted to all of us, so explicitly and so ungrammatically, that the proposed military action of his government, had it taken place, would have been illegal. And again, under the President’s own admission, it would have been illegal regardless of whether one embraces a more restrictive or a more expansive theory of self-defence.