This article examines civilian mobilization amidst the Donbas war, Ukraine. It focuses on ordinary residents of the frontline regions who voluntarily got together to address the humanitarian and military consequences of war in the environment of lacking state support. It explores the micro-level dynamics of mobilization, particularly the demographic profile of civilian volunteers, their motivations to join, and pathways to engagement. In so doing, it provides an account of how ordinary residents of seemingly passive regions – Southern and Eastern Ukraine – become active in times of crisis. Contrary to the mainstream accounts that credit civilian mobilization to the rise of patriotism in wartime, it demonstrates that local security concerns and affective reactions to the heightened precarity of others are crucial factors that propel collective action at the rear. In the case of Ukraine, the efficiency of wartime mobilization was increased through the structures that emerged during the proceeding Maidan protests, as well as preexisting private and entrepreneurial networks. By employing ethnographic tools of inquiry, the article interrogates the mobilizing potential of seemingly latent communities in times of crisis and contributes to the literature on wartime collective action at the rear.