The Photographic History of The Civil War: in ten volumes, Thousands of Scenes Photographed 1861-65, with Text by many Special Authorities, Volume 3: The Decisive Battles.
Francis Trevelyan Miller, Ed.

[16] Washington, the northern border of Virginia as far as Harper's Ferry, covered by the Army of the Potomac; across the mountains into West Virginia, to the headwaters of the Holston River in Tennessee, down that river and the Tennessee to Chattanooga, and thence along the Memphis and Charleston Railroad to the Mississippi, which was also in Union hands. All south of that line was in the hands of the Confederates, except a few stations along the sea coast, the possession of which assisted in the blockade.

Most of the opposing troops which were east of the Mississippi had been concentrated into the armies commanded by Lee and Johnston; that commanded by Lee facing the Army of the Potomac and guarding Richmond, while that of Johnston was at Dalton, in the northern part of Georgia, facing Sherman and defending Atlanta, a great railroad center and a point of concentration of supplies for the Confederate troops, wherever they were stationed, east of the Mississippi River. Richmond and the armies under Lee and Johnston were the main objectives of the campaign.

General Grant, as commander of the Union armies, placed himself with the Army of the Potomac, where the greatest opposition was to be expected, and where he considered his personal presence would be of the greatest value, and whence he exercised general supervision over the movements of all the armies.

The main movements being against Lee and Johnston, all other troops were directed to cooperate with the main armies. The movements of detached bodies would compel the Confederates either to detach largely for the protection of his supplies and lines of communication, or else to lose them altogether.

Everything being prepared, orders were given for the start, and all the armies were on the move by the 6th of May, with what results the chapters that follow will tell the reader in detail.