Kentucky was a southern border state of key importance in the American Civil War. It officially declared its neutrality at the beginning of the war, but after a failed attempt by Confederate General Leonidas Polk to take the state of Kentucky for the Confederacy, the legislature petitioned the Union Army for assistance. Though the Confederacy controlled more than half of Kentucky early in the war, after early 1862 Kentucky came largely under U.S. control. In the historiography of the Civil War, Kentucky is treated primarily as a southern border state, with special attention to the social divisions during the secession crisis, invasions and raids, internal violence, sporadic guerrilla warfare, federal-state relations, the ending of slavery, and the return of Confederate veterans.

Lieutenant-General Leonidas Polk was a bishop of the Episcopal Diocese of Louisiana and founder of the Protestant Episcopal Church in the Confederate States of America, which separated from the Episcopal Church of the United States of America. He was a planter in Maury County, Tennessee, and a second cousin of President James K. Polk. He resigned his ecclesiastical position to become a major-general in the Confederate States Army, when he was called "Sewanee's Fighting Bishop". His official portrait at the University of the South depicts him as a bishop with his army uniform hanging nearby. He is often erroneously referred to as "Leonidas K. Polk," but he had no middle name and never signed any documents as such.