What happens when partisanship is pushed to its extreme? In With Ballots and Bullets, Nathan P. Kalmoe combines historical and political science approaches to provide new insight into the American Civil War and deepen contemporary understandings of mass partisanship. The book reveals the fundamental role of partisanship in shaping the dynamics and legacies of the Civil War, drawing on an original analysis of newspapers and geo-coded data on voting returns and soldier enlistments, as well as retrospective surveys. Kalmoe shows that partisan identities motivated mass violence by ordinary citizens, not extremists, when activated by leaders and legitimated by the state. Similar processes also enabled partisans to rationalize staggering war casualties into predetermined vote choices, shaping durable political habits and memory after the war's end. Findings explain much about nineteenth century American politics, but the book also yields lessons for today, revealing the latent capacity of political leaders to mobilize violence.