The Unwilling and Unable Test for Extraterritorial Defensive Force

Abstract

Abstract This chapter focuses on the defensive use of force against non-state actors located on the territory of a third state. The legality of such operations is among the most contested legal questions of our time. Few states question the legality of using defensive force against non-state actors per se, but the more contested question is whether such interventions are illegal as to the third state on whose territory the non-state actor resides, and on whose territory the intervening state must necessarily engage in military action if it hopes to defeat the non-state actor. A number of states, though not all, have coalesced around the standard that such interventions are permissible if the territorial state is unwilling or unable to resolve the threat posed by the non-state actor. This chapter canvasses the existing conceptual rationales for the unwilling or unable test and discusses the plusses and minuses of each approach. This chapter then articulates a new conceptual justification, one that is arguably implicit in many articulations of the unwilling or unable test. This conceptual justification states that even if the intervening state violates the sovereignty of the territorial state, the territorial state is “estopped” from objecting to the violation, on account of the territorial state’s complicity or powerlessness with regard to the non-state state actor. It is asserted that this notion of “sovereignty estoppel” captures, in a nuanced way, the international community’s discomfort with these interventions but also the community’s all-things-considered judgment that such actions may be necessary in some contexts.