When Maj. Gen. James B. McPherson was killed in action during the Atlanta Campaign, command of Army of the Tennessee opened up, and when Hooker did not get it he resigned his commission. Maj. Gen. William T. Sherman appointed Slocum to command the XX Corps, which earlier had been formed by merging the XI Corps and XII Corps into a single command. His former XII Corps soldiers cheered their previous commander's return. When Atlanta fell to Sherman on September 2, 1864, Gen. Slocum and his corps were the first to enter the city.