In the summer of 1863, Union Maj. Gen. William Rosecrans maneuvered Gen. Braxton Bragg out of central Tennessee. Rosecrans captured the critical rail hub at Chattanooga and pursued Bragg into North Georgia. The two armies collided on September 19 along Chickamauga Creek. The next day Rosecrans mistakenly pulled a division out of line, opening a gap in the Union position. The Confederates exploited the breach and Rosecrans retreated to Chattanooga.