Recent years have seen the emergence of significant legal debate surrounding the use of force against armed groups located in other States. With time, it has become clear that in many cases such operations are not confined to the territory of one other State, but expand to encompass multiple territories and often more than one armed group. This article examines multi-territorial conflicts with armed groups through the lens of several legal frameworks. Among other topics, it analyses the questions surrounding the extension of self-defense into multiple territories, the classification of the hostilities with the group and between involved States, the scope of the battlefield, the use of terms such as “associated forces” in the context of armed groups, and the interplay with human rights law in such operations. This article sets out to draw together the threads of these debates in the last fifteen years and suggest a way forward for overcoming the legal challenges.