The conquest of Atlanta was the goal of Maj. Gen. William Tecumseh Sherman. After the victory at Missionary Hill, Sherman succeeded General Grant as Grant went on to become a Lt. General as the general in chief. At the time, Sherman was in Chattanooga, 100 miles to the north. Sherman led his toops against the troops of Confederate General Johnson and outflanked them, causing their withdrawl. The two armies skirmished for a few days, but eventually Sherman forced the confederate forces back to the Chattahochee River. He was now able to see his goal, the city of Atlanta, eight miles in the distance.
General John Bell Hood, now replaced Johnson in hopes that his more agressive tactics would prevail against Sherman. Confederate forces led by Hood and General Mcpherson failed to defeat Sherman as he began long range artillery fire as inhabitants of Atlanta began to flee. Sherman's army began one final flanking movement to the south, cutting the last remaining rail link to the city at Jonesboro. On September 2nd, Sherman's army entered Atlanta. In less than four months and at the cost of 31,000 casualties , the heart of the South had been taken.
Source: http://ngeorgia.com/history/battleofatlanta.html