Commissioned as a brigadier General, Buell assisted in organizing the Army of the Potomac before being charged with the Army of the Ohio. Buell's command succeeded in capturing Nashville, Tennessee in February 1862. Buell later commanded forces at Shiloh, Corinth, and Perryville. However, his failure to pursue the Confederate forces after Perryville led to his removal from command because of this inactivity. He resigned his commission on June 1, 1864.