Battle of Antietam

On September 9, 1862, Robert E. Lee split his army and sent Stonewall Jackson to capture Harpers Ferry. An excerpt from the article:

"On September 9, Lee issued Special Order 191 defining his “Maryland Campaign.” His plan to enter northern territory divided his army, sending each unit to march on a specific town: Boonsboro and Hagerstown in Maryland, and Harper’s Ferry and Martinsburg in West Virginia.

Special Order 191
After the Confederates abandoned their campsite around Frederick, McClellan’s army moved in. What happened next was pivotal: On September 13, two Union soldiers, Private Barton W. Mitchell and Sergeant John M. Bloss, discovered a copy of Special Order 191 with detailed Confederate troop movements, allegedly wrapped around three cigars.

Upon learning of the valuable find, an ecstatic McClellan reportedly exclaimed, “Here is a paper with which, if I cannot whip Bobby Lee, I will be willing to go home.” He immediately moved his army in hopes of foiling Lee’s battle plans.

And when Lee heard a copy of Special Order 191 was missing, he knew his scattered army was vulnerable and rushed to reunite its units.

On September 14, at the base of South Mountain near Sharpsburg, Confederate Generals D.H. Hill’s and James Longstreet’s units encountered Union resistance and sustained heavy casualties. Lee planned to retreat to Virginia, but changed his mind after hearing Confederate General Thomas Jonathan Jackson—better known as Stonewall Jackson—had captured Harper’s Ferry.

Instead, Lee ordered his army to regroup at Antietam Creek near Sharpsburg."