The Civil War is about to loom very large in the popular memory. We would do well to be candid about its causes and not allow the distortions of contemporary politics or long-standing myths to cloud our understanding of why the nation fell apart. The coming year will mark the 150th anniversary of the onset of the conflict, which is usually dated to April 12, 1861, when Confederate batteries opened fire at 4:30 a.m. on federal troops occupying Fort Sumter. Union forces surrendered the next day, after 34 hours of shelling.