Does the war-making/state-making thesis, most associated with Charles Tilly, apply in the developing world If so, how? This essay reviews the bellicist literature and offers an explanation for variation in state capacity among the most war-prone states in the developing world. We investigate the influence of war on state strength in two countries, Afghanistan and Vietnam. We examine three hypothesized causal mechanisms about how war contributes to state formation: raising money, building armies, and making nations. We find that war in Vietnam contributed to state-building, while war in Afghanistan has been state-destroying. There appear to be two main factors that contributed to state-making in Vietnam that were absent in Afghanistan: the existence of a core ethnic group that had served as the basis for a relatively long-standing political community in the past, and the combination of war and revolution, which inspired state officials and facilitated the promulgation of a unifying national ideology. Of these two factors, comparative data suggest relative ethnic homogeneity is the most important. Absent these specific conditions, war is more likely to break than make states in the contemporary Third World.