Previous research has implicitly assumed that civil wars represent a coherent category of events, but given the variety of rebel goals that supposition seems tenuous. We split civil wars into those where the rebels simply want to remove the government (replacement) from those where the rebels want to alter the relationship between the state and society (legitimacy). Theoretically, states are most at risk for a civil war of replacement when they extract substantial wealth from society and the government is weak. In contrast, civil wars of legitimacy are more likely to occur in states where the rebels have both grievances and a means to maintain their future viability. An empirical analysis of civil wars of replacement and legitimacy from 1960 to 1999 confirms both our argument about the different types of civil violence and their differing causes.