 When Lee decided to invade the North in the Maryland Campaign, Jackson took Harpers Ferry, then hastened to join the rest of the army at Sharpsburg, Maryland, where they fought McClellan in the Battle of Antietam (Sharpsburg).Antietam was primarily a defensive battle against superior odds, although McClellan failed to exploit his advantage.Jackson's men bore the brunt of the initial attacks on the northern end of the battlefield and, at the end of the day, successfully resisted a breakthrough on the southern end when Jackson's subordinate, Maj. Gen. A. P. Hill, arrived at the last minute from Harpers Ferry.