Lee's goal was for the Army of Northern Virginia to invade the Northern states of Maryland and Pennsylvania. That way he could threaten the cities of Washington, D.C. and Baltimore. By a series of decisive victories Lee thought that the South could gain recognition from England and France and get them to support the Southern cause. The hope was if Lee's army was victorious, it might cause Abraham Lincoln to sue for peace. During the month of September Lee had moved his army north. They captured the garrison at the Battle of Harpers Ferry. Lee's army was driven back at the Battle of South Mountain and withdrew again after a day of heavy fighting at Antietam. Retreating back into Virginia, Lee managed to reinforce General George B. McClellan's overly-cautious nature with a successful rearguard action at the Battle of Shepherdstown. It stopped the Union Army of the Potomac from chasing the Army of Northern Virginia back into Virginia. From a military standpoint, Antietam was a draw. But it gave Lincoln the opportunity he needed to claim a victory and use it to deliver his Emancipation Proclamation.