Buckner considered Union actions in Kentucky to be violations of the U.S. Constitution and of states' rights, so in September 1861 he went to Nashville, where he accepted Confederate General Albert Sidney Johnston's offer of a brigadier generalship. Johnston ordered Buckner to Fort Donelson, where a terribly confused situation left him in command. The Union forces enveloped that position, and in February 1862 Buckner surrendered the fort on the now-famous "unconditional surrender" terms of General Ulysses S. Grant. Buckner remained a prisoner for more than five months. After being exchanged he was promoted to major general and served capably in a number of battles, notably Perryville and Chickamauga. In 1864 Buckner joined the trans-Mississippi forces of General E. Kirby Smith and in September received promotion to lieutenant general.
Bennett H. Wall, "Buckner, Simon Bolivar," American National Biography Online, February 2000, http://www.anb.org/articles/05/05-00098.html.