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| image = [[File:
Rosecrans, William S.(1). jpg]]| caption = Portrait of Major General William S. Rosecrans from Delaware County, Ohio, ca. 1861-1865 . Photograph was made from a negative in Brady's National Portrait Gallery.
During the American Civil War, the Battle of Chickamauga took place from September 18 to September 20, 1863. The battle pitted the Union's Army of the Cumberland, commanded by General William Rosecrans of Ohio, against the Confederate's Army of Tennessee, commanded by General Braxton Bragg. The
Union army numbered approximately sixty thousand men, while the Confederates had forty-three thousand soldiers. The campaign that culminated in the Battle of Chickamauga began in June 1863. Following Bragg's defeat at the Battle of Stone's River in January 1863, the Confederates withdrew to the Tennessee River, just north of the city of Chattanooga, an important railroad center in southern Tennessee. Bragg believed that Rosecrans would next advance upon Chattanooga, hoping to seize the city. Rosecrans's Army of the Cumberland did advance southward. But rather than attacking Bragg's men at the Tennessee River, the Union force flanked the Confederates by crossing the river further south. Bragg's army retreated to Chickamauga Creek, where the Confederates waited to attack the Union soldiers. Thanks to reinforcements from Virginia, Mississippi, and Tennessee, Bragg's army now approached sixty-six thousand men. On September 19, 1864, the Union soldiers encountered the Confederate force, and the Battle of Chickamauga began. The Confederates fared well the first day of the battle, slowly driving the Union soldiers backwards in sometimes-fierce hand-to-hand combat. The battle continued on September 20, when the Confederates renewed the attack. A large number of Union troops, approximately one third of the army under Rosecrans's command, broke under an attack from General James Longstreet's Virginians. Union General George Thomas rallied part of the Union line against the Southern advance. These men stalled the Confederate attack, giving the retreating Union soldiers enough time to escape. Thomas retreated with his men that evening under the cover of darkness. In the battle, the Union lost 16,170 men to the Confederate’s 18,454 men killed, wounded or captured. The Army of the Cumberland regrouped at Chattanooga. Confederate forces seized the heights, including Missionary Ridge and Lookout Mountain, surrounding the city. Confederate artillery prevented supply trains or reinforcements from reaching Rosecrans's army, while it also prohibited the Union soldiers from retreating. The Union soldiers were in a dire situation. They had to surrender, starve, or attack a larger, well-fortified force. The stage was set for the Battle of Chattanooga. [[Category:History Events]]