I think he was quite right, for the war could not be decided by the possession of military posts or even of cities, for hostilities would never cease until one army or the other was destroyed.

He therefore applied to Washington for permission to add this force to that of Slocum, in order that the two might act directly against Lee's communications by following up his rear while preserving their own line of retreat.
Slocum had been already ordered there, for this purpose, but Halleck would not consent that the garrison of Harper's Ferry should be withdrawn under any circumstances, and positively refused Hooker's request.

Hooker then considering himself thwarted in all his plans by the authorities at Washington, offered his resignation.

It was promptly accepted, and Major-General George G.Meade, then the commander of the Fifth Corps, was assigned to the command of the Army of the Potomac.

He was a general of fine intellect, of great personal bravery, and had had a good deal of experience in the war in handling troops, but had never achieved any brilliant success, or met with any serious reverse.
Upon ascertaining that the enemy were at York and Carlisle, Hooker had determined to throw out his different corps in a fan shape toward the Susquehanna, and advance in that direction with three corps on the left to defend that flank, in case Longstreet and Hill should turn East, instead of keeping on toward the North.