The Army of the Potomac was a separate command and had no territorial limits.

There were thus seventeen distinct commanders.
Before this time these various armies had acted separately and independently of each other, giving the enemy an opportunity often of depleting one command, not pressed, to reinforce another more actively engaged.

I determined to stop this.

To this end I regarded the Army of the Potomac as the centre, and all west to Memphis along the line described as our position at the time, and north of it, the right wing; the Army of the James, under General Butler, as the left wing, and all the troops south, as a force in rear of the enemy.

Some of these latter were occupying positions from which they could not render service proportionate to their numerical strength.