The Photographic History of The Civil War: in ten volumes, Thousands of Scenes Photographed 1861-65, with Text by many Special Authorities, Volume 2: Two Years of Grim War.
Francis Trevelyan Miller, Ed.

In the campaign we are describing Jackson was the most active and conspicuous figure on the Confederate side. He rested at Gordonsville for two weeks, recuperating his health and that of the army, which had been much impaired in the malarial district of the Peninsula. The fresh mountain air blowing down from the Blue Ridge soon brought back their wonted vigor. On July 27th A. P. Hill was ordered to join him, and the Confederate leader now had about twenty-five thousand men.

The movement on Gordonsville was exactly in accordance with Jackson's own ideas which he had urged upon Lee. Although believing McClellan to be in an impregnable position on the Peninsula, it was not less evident to him that the Union general would be unable to move further until his army had been reorganized and reenforced. This was the moment, he argued, to strike in another direction and carry the conflict into the Federal territory. An army of at least sixty thousand should march into Maryland and appear before the National Capital. President Davis could not be won over to the plan while McClellan was still in a position to be reenforced by sea, but Lee, seeing that McClellan remained inactive, had determined, by sending Jackson westward, to repeat the successful tactics of the previous spring in the Shenandoah valley. Such a move might result in the recall of McClellan.

And so it happened. No sooner had Halleck assumed command of all the Northern armies than the matter of McClellan's withdrawal was agitated and on August 3d the head of the Army of the Potomac, to his bitter disappointment, was ordered to join Pope on the Rappahannock. Halleck was much concerned as to how Lee would act during the Federal evacuation of the Peninsula, uncertain whether the Confederates would attempt to crush Pope before McClellan could reenforce him, or whether McClellan would be attacked as soon as he was out of his strong entrenchments at Harrison's Landing.