A campaign during the American Civil War. On 9 September a Federal army under General W. Rosecrans occupied Chattanooga, a strategic communication centre for the Confederacy and pushed on south-eastwards. Rosecrans’s forces were attacked by a Confederate army under General Bragg, who successfully drove Rosecrans back to Chattanooga, where the Union army was besieged for several weeks. General Ulysses Grant assumed direct command, broke the siege and counter-attacked, winning the Battle of Chattanooga and opening the way for the advance on Atlanta (1864) and later for the march of General William Sherman to the sea.