The Battle of Antietam, also known as the Battle of Sharpsburg, was fought on September 17, 1862, near Sharpsburg, Maryland, during the American Civil War. It marked the first major battle of the war to take place on Union soil and became the bloodiest single day in American history, with around 23,000 soldiers killed, wounded, or missing. Union forces under General George B. McClellan clashed with Confederate troops led by General Robert E. Lee, who had invaded Maryland in hopes of gaining support from European powers and encouraging border states to join the Confederacy. The battle ended tactically inconclusive, but Lee’s retreat back to Virginia gave President Abraham Lincoln a strategic victory. This allowed Lincoln to issue the preliminary Emancipation Proclamation, which reframed the war as a fight against slavery and discouraged foreign nations from aiding the Confederacy.