After winning a victory at Chickamauga in September 1863, the Confederates besieged Chattanooga but were finally driven off by Grant in November. Many of the Confederate defeats can be attributed to the poor leadership of General Braxton Bragg, who led the Army of Tennessee from Shiloh to the Confederate defeat in the Chattanooga campaign. Historian Thomas Connelly concludes that although Bragg was an able planner and a skillful organizer, he failed repeatedly in operations, in part because he was unable to collaborate effectively with his subordinates.