On January 3, 1861, at the onset of tensions which would lead to the
Civil War later that April, Harrison entered the
Confederate States Army as
second lieutenant of the First Georgia Regulars. He later participated in the
seizure of Fort Pulaski. After reaching the rank of Brigadier General, Harrison commanded a brigade of
A.P. Stewart's corps. At the time, he was 23 years old, the youngest Brigadier-General in the Confederate Army. During the course of the war, Harrison was wounded three times. The last time at the Battle of Olustee, where a horse was shot out from under him. Harrison commanded a prison camp at
Florence, South Carolina, in late 1864, where 25,000 Union prisoners were interned. He was commended by Union prisoners for his humane treatment of them. During the war, Harrison undertook the command responsibility of brigadier general, leading a brigade during the
Carolinas campaign and at the
Battle of Bentonville, and elsewhere. Although he received a provisional appointment to that rank, it was never officially confirmed before the end of hostilities. ==Legal and political career==