Little attention has been paid to the social processes of civil war—the transformation of social actors, structures, norms, and practices—that sometimes leave enduring legacies for the postwar period. In this article, I explore the changes wrought by six social processes: political mobilization, military socialization, polarization of social identities, militarization of local authority, transformation of gender roles, and fragmentation of the local political economy. Some of these social processes occur in peacetime, but war may radically change their pace, direction, or consequences, with perhaps irreversible effects. I trace the wide variation in these processes during the wars in four countries: Peru, El Salvador, Sri Lanka, and Sierra Leone. I analyze the effects of these processes as transformations in social networks. These processes reconfigure social networks in a variety of ways, creating new networks, dissolving some, and changing the structure of others.