Internal war exacts a devastating toll on societies. Yet among countries that have gone through civil wars, striking variation exists simply in the length of exposure to violence. This paper develops a theory of decision-making by armed groups that explains why some civil wars are so persistent, and tests it using evidence gathered during field research on the Lebanese Civil War, 1975-1990. The theory links local actions of armed groups to the macro-level process alliance with and support from external actors. In the presence of international competition, external involvement can become intense and widespread. External support constitutes a subsidy to armed groups, especially their leaders. The result is that for the leadership war is no longer a costly enterprise: the provision of external support to armed internal actors generates benefits for their leaders that exceed any possible share of the peacetime economy available to them. The paper focuses on logic of the actions of the armed internal actors: what is the effect of subsidies on the decisions of armed groups about whether to continue fighting? How do leaders, who are singular beneficiaries of external support, maintain order within their groups such that their followers, both fighters and the civilian constituency, remain mobilized behind them to continue in the war? The mechanisms of this theory are established drawing on interviews the author conducted with mid-level commanders who fought on all sides in the Lebanese Civil War. Observable implications of the theory are then tested using a neighborhood-level dataset which was collected specifically for this project, covering armed groups' daily activities for the first year of the war. These concern two sets of wartime behaviors that are linked to these subsidies: alliances and the nature of the use of military force. First, there is a link between external support and the behavior of actors who are allied on one side of a macro-level cleavage. Second, external support cushions against the pressures of competition and the potential for elimination by force, inducing a type of conflict characterized by fighting without warfare.