How the unprepossessing Ulysses S. Grant, whose military genius ultimately preserved the Union, came to the forefront in the Civil War is a story as surprising as it is compelling. Forced to resign his commission in the peacetime army for drinking, and thereafter reduced to eking out a living for himself and his family with hardscrabble jobs, at the outbreak of hostilities he suddenly found himself a colonel, and then a general, of volunteers. Grant...