The Battle of Chickamauga, fought on September 18–20, 1863, between the United States Army and Confederate forces in the American Civil War, marked the end of a U.S. Army offensive, the Chickamauga Campaign, in southeastern Tennessee and northwestern Georgia. It was the first major battle of the war fought in Georgia, the most significant US defeat in the Western Theater, and involved the second-highest number of casualties after the Battle of Gettysburg.

The Army of Tennessee was the principal Confederate army operating between the Appalachian Mountains and the Mississippi River during the American Civil War. It was formed in late 1862 and fought until the end of the war in 1865, participating in most of the significant battles in the Western Theater.