 Complete the following phrase:  Having forced Bragg to evacuate Chattanooga on September 6 through a series of skillful maneuvers, Rosecrans ordered his army to advance along three different roads into northwestern Georgia in pursuit of the Army of Tennessee. With the Federals divided and unable to support each other due to the mountainous terrain, Bragg chose to concentrate on one Union corps, the XIV Corps, which had advanced through the same gap taken by the 33rd at Pigeon Mountain and adjacent passes, and was moving toward Lafayette. An abortive assault launched by Cleyburnes and Hindmans divisions at Daviss Cross Roads allowed the Federals to escape to safety, so Bragg now turned north, where Rosecrans main force was rapidly concentrating at Lee and Gordons Mill along Chickamauga Creek. Having been promised three extra divisionsincluding two led by the renowned Lieutet General James LongstreetBragg decided to attack Rosecrans army. Skirmishing commenced on September 18, with the main 