It turned out that the second battle of Bull Run had by no means so seriously disorganized the Union army as was reported, and that Washington had been exposed to no real danger. The Confederate army hovered on its front for a day or two, but made neither attack nor demonstration. Instead of this, Lee entered upon a campaign into Maryland, hoping that his presence might stimulate a secession revolt in that State, and possibly create the opportunity successfully to attack Baltimore or Philadelphia.
Pope having been relieved and sent to another department, McClellan soon restored order among the troops, and displayed unwonted energy and vigilance in watching the movements of the enemy, as Lee gradually moved his forces northwestward toward Leesburg, thirty miles from Washington, where he crossed the Potomac and took position at Frederick, ten miles farther away. McClellan gradually followed the movement of the enemy, keeping the Army of the Potomac constantly in a position to protect both Washington and Baltimore against an attack. In this way it happened that without any order or express intention on the part of either the general or the President, McClellan's duty became imperceptibly changed from that of merely defending Washington city to that of an active campaign into Maryland to follow the Confederate army.
This movement into Maryland was begun by both armies about September 4. On the thirteenth of that month McClellan had reached Frederick, while Lee was by that time across the Catoctin range at Boonsboroa, but his army was divided. He had sent a large
