The first major battle of the Civil War was fought in Georgia, from September the 18th-20th 1863. The Battle of Chickamauga was the most significant Union defeat in the western theatre and had the second highest number of casualties of any civil war battle, after the Battle of Gettysburg. The army of the Cumberland under Major General William Rosecrans engaged the Confederate Army of Tennessee under General Braxton Bragg. In early September Rosecrans had forced Bragg's army out of Chattanooga