From the hills and valleys of the eastern Confederate states to the sun-drenched plains of Missouri and "Bleeding Kansas," a vicious, clandestine war was fought behind the big-battle clashes of the American Civil War. In the east, John Singleton Mosby became renowned for the daring hit-and-run tactics of his rebel horsemen. Here a relatively civilized war was fought; women and children usually left with a roof over their heads. But along the Kansas-Missouri...