The Battle of Antietam took place in Maryland in September 1862 and was the first battle to occur on northern soil. Confederate General Robert E. Lee had led his army into the North, hoping a successful invasion would weaken Northern morale, encourage European nations to support the Confederacy, and possibly convince Maryland to join the Southern cause. It became the bloodiest one-day battle in American history, with nearly 23,000 casualties (killed or wounded). After intense and deadly fighting, Confederate forces withdrew, signaling a Union victory. This victory boosted Union confidence and gave President Lincoln the motivation to move forward with the Emancipation Proclamation, which would soon change the goals of the war and strengthen the Union army.