Bragg was in the full tide of his temporary success in Tennessee and Kentucky, and, after his great victory of Second Bull Run, Lee naturally invaded Maryland, which, it was assumed, had not forgotten its Southern sympathies. But Lee received no real accession of strength, and when McClellan with all available forces moved out of Washington to encounter the Army of northern Virginia, the Confederates were still but a few marches from the point where they had crossed the Potomac. Lee had again divided his army.

On the 13th of September Jackson was besieging 11,000 Federals in Harper's Ferry, Longstreet was at Hagerstown, Stuart's cavalry holding the passes of the South Mountain, while McClellan's whole army lay at Frederick. Here extraordinary good fortune put into the enemy's hands a copy of Lee's orders, from which it was clear that the Confederates were dangerously dispersed. Had McClellan moved at once he could have seized the passes without difficulty, as he was aware that he had only cavalry to oppose him. But the 13th was spent in idleness, and stubborn infantry now held the passes.

A serious and costly action had to be fought

A serious and costly action had to be fought before the way was cleared (battle of South Mountain, September 14). On the following day Harper's Ferry capitulated after a weak defence. Jackson thereupon swiftly rejoined Lee, leaving only a division to carry out the capitulation.

On the 16th McClellan found Lee in position behind the Antietam Creek, and on the 17th was fought the sanguinary and obstinately contested battle of Antietam or Sharpsburg. At the price of enormous losses both sides escaped defeat in the field, but Lee's offensive was at an end and he retired into Virginia. Thenceforward the Confederacy was purely on the defensive. Only twice more did the forces of the South strike out (Gettysburg, 1863; Nashville, 1864), and then the offensive was more of a counter-attack than an advance.

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