By crossing the Potomac and invading Maryland. On September 4, 1862, the Army of Northern Virginia crossed at Leesburg and headed toward Frederick.. This movement had long been desired by Confederate leaders, who believed Maryland would rise to become the twelfth Confederate state. There was a popular song, “Maryland, My Maryland!” that had been composed with this in mind, and the Confederate bands played it as the men crossed the Potomac. Many observers claimed this was the high point of the war for the Confederacy.

Their sight was good, but their knowledge was incomplete. Aside from the desire to win a major battle on Northern soil, Robert E. Lee was practically forced to invade because his army was close to starvation. The lands of Northern Virginia, especially in the vicinity of Bull Run, had been picked over and devastated by crossing armies so many times there was no food, milk, or well water to be had. Maryland, by comparison, offered large expanses of land and fields and farms which had not yet felt the hand of war.