Because they are chiefly domestic conflicts, civil wars have been studied primarily from a perspective stressing domestic factors. We ask, instead, whether (and how) the international system shapes civil wars; we find that it does shape the way in which they are fought—their “technology of rebellion.” After disaggregating civil wars into irregular wars (or insurgencies), conventional wars, and symmetric nonconventional wars, we report a striking decline of irregular wars following the end of the Cold War, a remarkable transformation of internal conflict. Our analysis brings the international system back into the study of internal conflict. It specifies the connection between system polarity and the Cold War on the one hand and domestic warfare on the other hand. It also demonstrates that irregular war is not the paradigmatic mode of civil war as widely believed, but rather is closely associated with the structural characteristics of the Cold War.