What leads armed groups to continue fighting, even in the face of extensive attempts at negotiated settlements or imposed military solutions? The rich information available on armed group activities in conflicts contrasts with few systematic explanations of this behavior. Yet, systematic models fail to account for the environment in which armed groups operate in explaining their actions. My dissertation proposes a new theory of the dynamics of civil war duration and termination that combines the systemic with in-depth knowledge of conflict. How actors benefit from opportunities that exist only during conflict explains duration and termination of conflict. Actors exploit opportunities during wartime which are unique in that they are outside the set of all possible peacetime allocations. Wars continue when, conditional on survival, actors remain able to exploit these opportunities. I investigate this theory through field research on the Lebanese Civil War, 1975-1990, that gathers information using parallel qualitative and quantitative strategies. I will conduct extensive interviews with leaders and members of armed groups and civilians to assess the theory’s implications about actors’ motivations and beliefs. I will also collect a database on armed groups to use in statistical panel analyses to assess the theory’s ability to explain the dynamics of conflict. I choose to research Lebanon because the multiple dimensions of warfare and political issues at play allow me to examine in one conflict what would researchers would have to explore in many separate conflicts. I also place the Lebanese Civil War within the universe of civil wars so that I can set scope conditions on the empirical results. This research design and its results fit into a larger research program that aims to generate and test a better theory of the dynamics of civil wars that can explain outcomes during conflict and their effects on the post-conflict situation.