risk was great, and Mr. Lincoln could not sanction it. He wrote: "I
think Lee's army, and not Richmond, is your sure objective point. If he
comes towards the Upper Potomac, follow on his flank and on his inside
track, shortening your lines while he lengthens his; fight him, too,
when opportunity offers. If he stays where he is, _fret him, and fret
him_."

This was good strategy and was adopted for the campaign. Ewell's corps
crossed the Upper Potomac, and on June 22 was in Pennsylvania. The
corps of Longstreet and Hill quickly followed, and Lee's triumphant
army, at least 70,000 strong, marched through the Cumberland Valley to
Chambersburg and Carlisle, gathering rich booty of herds and grain as
they went, with Harrisburg as an immediate objective, Philadelphia in no
remote distance, Baltimore and Washington in a painfully distinct
background. The farmers of western Pennsylvania, startled by the
spectacle of gray-coated cavalry riding northward towards their state
capital, cumbered the roads with their wagons. The President called from
the nearest States 120,000 militia. General Hooker, released from his
waiting attitude by the development of his adversary's plan, manoeuvred
well. He crossed the Potomac at Edwards' Ferry, June 25-26, and drew his
forces together at Frederick. It was then decided to move northward and
to keep Lee as well to the westward as possible, thereby reserving, for
the bearing of future events, the questions of cutting the Confederate
communications or bringing on a battle.

An unfortunate element in these critical days was that Halleck and
Hooker disliked each other, and that their ideas often clashed. Mr.
Lincoln was at last obliged to say to Hooker: "To remove all
misunderstanding, I now place you in the strict military relation to
General Halleck of a commander of one of the armies to the