SPECIAL ORDER 191: RUSE OF WAR©
On September 5, 1862, General Lee crossed his army over the Potomac into Western Maryland. It had taken him four months to drive Lincoln's armies out of Virginia and the effort had left his soldiers staggering. He needed to get them into the Shenandoah Valley, the only place within a radius of sixty miles from his position, after the fierce battle at Manassas, where they could find subsistence, rest, and reorganize. But, in turning his army back from the environs of Washington, it was impossible for him to lead it directly across the Blue Ridge into the Valley. Lincoln's armies would consolidate under McClellan's command again and move toward Richmond, and he would have to hurry his soldiers across the wasteland of Northern Virginia to intercept them. Only one strategy would keep the enemy away from Richmond while he marched his army to the Valley and that was to move there indirectly, through Maryland.
Twelve days after General Lee's army entered Maryland, the Battle of Antietam was fought on Constitution Day. In the space of twelve hours, over five thousand soldiers, blue and gray, lost their lives in action and another twenty thousand were wounded. Soon after, General Lee's soldiers were safely in the Shenandoah Valley, camped along the Opequon, where they remained until the end of October.
Since the end of the Civil War, generations of historians, as well as popular Civil War writers, have offered the view that the Battle of Antietam happened by accident, that in entering Maryland General Lee had planned to carry the war into Pennsylvania, drawing McClellan after him, but someone—perhaps one of General Lee's division commanders, D.H. Hill—had negligently lost a copy of Lee's movement order, which allowed McClellan to thwart Lee's plans and force him into battle at Sharpsburg. Yet, in light of all the available evidence, it seems reasonably clear that the Battle of Antietam happened by General Lee's design—a design that he formulated, in collaboration with Stonewall Jackson, while they were camped at Frederick, Maryland.