When Robert E. Lee divided his forces in Maryland, he sent nearly half to capture Harpers Ferry, and took most of the rest to Hagerstown in order to connect with his alternate supply base in Winchester. He left Daniel Hill’s division at South Mountain, guarding “the back door”, confident that he would accomplish his new objectives before George McClellan’s Army of the Potomac could threaten his divided army. Things didn’t quite turn out that way for him
