Antietam DLC contains:

• 20 Antietam Single player scenarios plus 1 Multiplayer scenario

• 8 South Mountain Single player scenarios plus 2 Multiplayer scenarios.

• 3 remastered maps

• 3 new OOBs

The Battle of Antietam, or Battle of Sharpsburg, as it was known in the South, was fought on September 17, 1862, along Antietam Creek, near the small farming community of Sharpsburg, Maryland.  The battle was part of General Robert E. Lee's Maryland Campaign and was the first major battle to take place in Union territory.  It was the bloodiest single day in American history, with around 23,000 casualties.

Shortly after Lee launched his Maryland Campaign, McClellan's Army of The Potomac cautiously left their camps near Washington, D.C., and pursued Lee into western Maryland.  On September 13th, when McClellan's army was encamped in Frederick, Maryland, Union soldiers discovered "Order 191" a detailed campaign plan outlining the movements of Lee's forces.  This document offered an opportunity to completely destroy Lee's Army of Northern Virginia, yet the timid McClellan acted slowly and did not take full advantage of it.

On September 14th, McClellan did manage to surprise a portion of Lee's army guarding the South Mountain gaps, where he achieved a decisive victory.  McClellan, however, did not capitalize on his success--instead of pursuing Lee's forces over the mountain, he halted, allowing Lee's army to concentrate on the high ground west of the Antietam Creek.

This set the stage for the largest battle of the Civil War up to that point.  Once again, McClellan acted timidly and stalled for nearly two days, giving Lee valuable time to reinforce his lines.  General "Stonewall" Jackson's force had captured Harpers Ferry on September 15th, and portions of Jackson's command were still making their way to Sharpsburg. 

By the morning of September 17th, all of Lee's divisions were deployed on good defensive ground near Sharpsburg, minus A.P. Hill's Division, which had been left to parole the Union prisoners at Harpers Ferry.  That afternoon, at the climax of the fighting, Hill arrived just in time to provide a crushing flank attack on the Union left, which ended the Battle of Antietam in a stalemate.