In past week, Kenya has conducted air strikes in Somalia against al Shabaab. Israel has undertaken airstrikes in Syria against Syrian military targets in response to a cross-border attack that killed an Israeli teenager. And the Syrian air force reportedly has carried out air strikes in western Iraq against ISIS. Each of these actions seems to have been taken in reliance on a theory of self-defense, and at least the first two strikes took place without the consent of the host state. (It is not clear whether Iraq consented to Syrian air strikes against ISIS.) But in none of these cases did the state using force submit an Article 51 letter to the U.N. Security Council. Nor does it appear that these states provided a less formal form of notification to the UNSC (though if readers know otherwise, I'd welcome correction).
Article 51 states, in relevant part, “Nothing in the present Charter shall impair the inherent right of individual or collective self-defence if an armed attack occurs against a Member of the United Nations, until the Security Council has taken measures necessary to maintain international peace and security. Measures taken by Members in the exercise of this right of self-defence shall be immediately reported to the Security Council.”
Article 51 letters generally inform the Security Council of the military action taken, as well as the legal rationale for the action and the circumstances that prompted it. These letters give other states – as well as the Security Council itself – the opportunity to respond, whether by expressing concern about the initial action, condoning it, or raising additional questions about it. A non-response by other states also may signal international support for the act of self-defense. Further, the ICJ noted in the Nicaragua case that a state’s failure to report under Article 51 can undermine the credibility of its self-defense claim.
It’s not clear why Syria, Israel, and Kenya have not submitted Article 51 letters. Maybe it’s an oversight. Maybe they would prefer to avoid having to defend their actions in writing. Maybe Kenya and Syria seek plausible deniability. (Israel has confirmed its actions publicly.) But Article 51 letters allow international law on the use of force to develop in a clearer, more comprehensive way, and the Security Council should insist on stricter compliance with the Charter’s reporting requirement. The UNSC could issue a resolution reminding states of their reporting obligations, or the President of the Security Council could make a statement to that effect. Either way, states that have decided to use force across borders without consent should explain their actions publicly, and the UNSC serves as the key forum in which to do so.