Self-defense may never be invoked to justify an act of retaliation or revenge in response to an unlawful threat that is no longer ongoing or imminent. So was the U.S. right to point to self-defense in justifying a strike against Iran following the shootdown of a U.S. drone?
More than any other policy area, the conduct of security affairs implicates legal systems beyond our own domestic law. Despite a deep-seated American distrust of international law, a web of international norms, treaties and agreements compels the United States to defend its conduct in terms intelligible to the world at large. As policymakers grapple with issues from cyberwar to targeted killings, legal expertise in international humanitarian law, the law of armed conflict, and a myriad other areas of international law will only become more crucial.