The Battle of South Mountain took place on September 14, 1862, during the American Civil War. It was a series of skirmishes fought between the Union forces, led by General George B. McClellan, and the Confederate army under General Robert E. Lee. The battle was significant as it allowed Union troops to gain control of the vital passes through the South Mountain range in Maryland. This battle was part of the larger Maryland Campaign, which aimed to relieve pressure on the Confederate forces and secure a victory on Northern soil. The Union's success at South Mountain helped set the stage for the subsequent Battle of Antietam, which would become one of the bloodiest days in American history.