President/Executive Department Commons^™

Co-Belligerency, Rebecca Ingber

Faculty Scholarship

Executive branch officials rest the President’s authority in today’s war against ISIS, al Qaeda, and other terrorist groups on an expansive interpretation of a 15-year-old statute, the 2001 “Authorization for Use of Military Force” (AUMF), passed in the wake of the 9/11 attacks. They rely on that statute to justify force against groups neither referenced in – nor even in existence at the time of – the 2001 statute, by invoking a creative theory of international law they call “co-belligerency.” Under this theory, the President can read his AUMF authority flexibly, to justify force against not only those groups covered …