How civilians respond to political violence profoundly shapes conflict processes and the legacies of civil war. Yet influential patterns of wartime civilian agency remain strikingly unexplored. This study investigates how exposure to state violence influences the organization of ordinary citizens into civil defense forces, a common and consequential type of mobilization that is still poorly understood. I argue that state violence marked by direct and collective targeting promotes community-based armed mobilization through the mechanisms of signaling and the militarization of local governance in irregular civil war. The analysis focuses on the Peruvian armed conflict during the 1980s. Based on an instrumental variable and a difference-in-differences approach, the results suggest that communities victimized by state forces were more likely to rise up against the insurgents at later stages. These counterintuitive findings underscore the relevance and complexity of grassroots collective action during war.