When Louisiana seceded, Sherman resigned as the superintendent of the state military academy. In May, he rejoined the U.S. army as a colonel. Sherman led a brigade in in the Battle of First Manassas. In August, he was made a brigadier general of volunteers and sent to Kentucky. In October, Sherman was put in command of the Dept. of the Cumberland, however, in November, he was transferred to the Dept. of the Missouri. Sherman distinguished himself as a division commander at Shiloh, and thus, he was promoted to major general in May. After the occupation of Memphis, Sherman took command of the District of Memphis from October through December 1862. After his defeat at Chickasaw Bluffs, he served in the capture of Arkansas Post.
When Ulysses S. Grant assumed supreme command in the West, Sherman became commander of the Army of the Tennessee. He commanded the Union left in the Chattanooga campaign before he moved to Knoxville, to the relief of Gen. Burnside. In March 1864, when Grant became commander in chief, Sherman succeeded him as supreme commander in the West. His Atlanta campaign resulted in the fall of that city on September 2, 1864. Sherman burned through the city, and, with 60,000 men, began his famous march to the sea. Savannah fell on December 21st. In February 1865, Sherman started northward, through South Carolina. In North Carolina, General Joseph E. Johnston opposed Sherman in engagements at Averasboro and Bentonville, but after hearing of Lee's surrender, he surrendered to Sherman.