American Civil War: The Battle of Chickamauga began in northwestern Georgia and would end in the most significant Union defeat in the Western Theater.

The American Civil War was a civil war in the United States between the Union and the Confederacy, which was formed in 1861 by states that had seceded from the Union. The central conflict leading to war was a dispute over whether slavery should be permitted to expand into the western territories, leading to more slave states, or be prohibited from doing so, which many believed would place slavery on a course of ultimate extinction.

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 and the most significant US defeat in the Western Theater, and it involved the second-highest number of casualties after the Battle of Gettysburg.

Georgia is a state in the Southeastern United States. It borders Tennessee and North Carolina to the north, South Carolina and the Atlantic Ocean to the east, Florida to the south, and Alabama to the west. Of the 50 U.S. states, Georgia is the 24th-largest by area and eighth most populous. According to the U.S. Census Bureau, its 2024 estimated population was 11,180,878. Atlanta, a global city, is both the state's capital and its largest city. The Atlanta metropolitan area, with a population greater than 6.3 million people in 2023, is the eighth most populous metropolitan area in the United States and contains about 57% of Georgia's entire population. Other major metropolitan areas in the state include Augusta, Savannah, Columbus, and Macon.

During the American Civil War, the United States Army, the land force that fought to preserve the collective Union of the states, was often referred to as the Union army, the federal army, or the northern army. It proved essential to the restoration and preservation of the United States as a working, viable republic.