In the Civil War, rough-and-tumble St. Louis played a key role as a strategic staging ground for the Union army. A citadel of free labor in a slave state, it also harbored deeply divided loyalties that mirrored those of its troubled nation. Until now, however, the fascinating story of wartime St. Louis has remained largely unchronicled. By the mid-nineteenth century, St. Louis had become the nation's greatest inland city, providing a "gateway...