During the Civil War, Buell was given command of a division of the Army of the Potomac and in November he succeeded William Sherman as head of the Department of the Ohio. He was also commander of the Army of the Cumberland prior to William S. Rosecrans.
At the Battle of Shiloh, he reinforced General Ulysses S. Grant, helping him defeat the Confederates, April 6, 1862. In July and August, the Confederates, under General Braxton Bragg, forced General Buell to abandon part of Kentucky. Although Bragg retreated in October, Buell did not follow him. On this account, his command was taken from him. He was replaced by William S. Rosecrans.
See also: Fort Donelson