This enforced retreat was not without effect on the morale of either army.  McClellan was as exultant as he was credulous.  “I have just learned,” he reported to Halleck at 8 A.M. on the 15th, “from General Hooker, in advance, that the enemy is making for Shepherdstown in a perfect panic; and that General Lee last night stated publicly that he must admit they had been shockingly whipped.  I am hurrying forward to endeavour to press their retreat to the utmost.”  Then, two hours later:  “Information this moment received completely confirms the rout and demoralisation of the rebel army.  It is stated that Lee gives his losses as 15,000.  We are following as rapidly as the men can move."* (* O.R. volume 19 pages 294, 295.) Nor can it be doubted that McClellan’s whole army, unaccustomed to see their antagonists give ground before them, shared the general’s mood.* (* “The morale of our men is now restored.”  McClellan to Halleck after South Mountain.  O.R. volume 19 part 2 page 294.) Amongst the Confederates, on the other hand, there was some depression.  It could not be disguised that a portion of the troops had shown symptoms of demoralisation.  The retreat to the Antietam, although effectively screened by Fitzhugh Lee’s brigade of cavalry, was not effected in the best of order.  Many of the regiments had been broken by the hard fighting on the mountain; men had become lost in the forest, or had sought safety to the rear; and the number of stragglers was very large.  It was not, then, with its usual confidence that the army moved into position on the ridge above the Antietam Creek.  General Longstreet, indeed, was of opinion that the army should have recrossed the Potomac at once.  “The moral effect of our move into Maryland had been lost by our discomfiture at South Mountain, and it was evident we could not hope to concentrate in time to do more than make a respectable retreat, whereas by retiring before the battle [of Sharpsburg] we could have claimed a very successful campaign."* (* Battles and Leaders volume 2 pages 666, 667.) So spake the voice of prudence.  Lee, however, so soon as he was informed of the fall of Harper’s Ferry, had ordered Jackson to join him, resolving to hold his ground, and to bring McClellan to a decisive battle on the north bank of the Potomac.

Although 45,000 men—­for Lee at most could count on no more than this number, so great had been the straggling—­were about to receive the attack of over 90,000, Jackson, when he reached Sharpsburg on the morning of the 16th, heartily approved the Commander-in-Chief’s decision, and it is worth while to consider the reasons which led them to disagree with Longstreet.