In Lincoln and California Brian McGinty explains the relationship between Abraham Lincoln and the Golden State, describing important events that took place in California and elsewhere during Lincoln's lifetime. He includes the histories of Lincoln's close friends and personal acquaintances who made history as they went to California, lived there, and helped to keep it part of the imperiled Union.

McGinty demonstrates that California was in large part responsible for beginning the Civil War, as the principal purpose of its conquest in the Mexican War was to acquire land into which the Southern states could extend their cotton-growing and slaveholding empire. The decision of California's first voters to exclude slavery from the state but to enact virulently racist legislation encouraged Southerners' hope that, if they established a separate republic, it would become an independent slave nation with the power to extend its territory to the Pacific coast of North America and into the Caribbean and Latin America. Lincoln's opposition to their plans unleashed the Civil War. As the struggle played out, the hopes of the proslavery Confederates were ultimately defeated because California played a vital role in helping Lincoln save the Union. Lincoln and California shines new light on an important state, a pivotal president, and a turning point in American history.