American Battlefield Trust's map of the Maryland Campaign
Following the success of the battle of Second Manassas, Confederate General Robert E. Lee sought to bring the war to Northern soil. Lee hatched a bold plan in which he divided his numerically inferior force in order to strike simultaneously into western Maryland and seize the Federal arsenal at Harpers Ferry. The Union Army of the Potomac is still licking its wounds from the Manassas fight when Lee's invasion commences. President Lincoln, anxious to spur the lethargic Federal host into action, restores Maj. Gen. George B. McClellan to command of the Potomac Army, which immediately begins its pursuit of the invading Rebels. Fortune favors McClellan when a mislaid Confederate communique (Special Order No. 191) falls into Union hands. Aware that Lee's forces are divided, McClellan prepares to offer battle on the banks of the Antietam Creek, near a town called Sharpsburg. The September 17 engagement is the bloodiest battle of the war to date, with no clear victor on either side. Lee, however, is forced to abandon his invasion of Maryland and the dubious Union victory gives Lincoln the political clout needed to issue the Preliminary Emancipation Proclamation.