A decisive engagement in the civil war occurred when northern General McClellan turned back general lee's army at?

A decisive engagement in the Civil War occurred when Northern General George B. McClellan turned back General Robert E. Lee's army at the Battle of Antietam on September 17, 1862. This battle is notable for being the bloodiest single-day conflict in American history, resulting in over 22,000 casualties. Although McClellan's forces were unable to pursue Lee's army effectively afterward, the battle provided a strategic victory for the Union and gave President Abraham Lincoln the opportunity to issue the Emancipation Proclamation.