At the end of the war, it was Grant. Prior to him had been Scott, Halleck, McClellan, Pope, Burnside, Hooker, and Meade.
There were at times several Union armies operating in the Eastern Theater of the US Civil War. The main one was the Army of the Potomac. Other Union armies in the east were the Army of the James, and the Army of Virginia.
The Army of the Potomac.
George.B.Mclellan headed the Union Army of the east.
Army of the Potomac
Army of the Potomac
Army of Northern Virginia
Grant concentrated on Lee in Virginia, and told Sherman to destroy Johnston's Army in Tennessee.
George McClellan
George McClellan
George McClellan
The main goal of the Union army in the east was to not be defeated by the Confederacy. This was the main goal of the entire Union Army from 1861 to 1864.
Basically everything south of Virginia (West Virginia was in the Union) and East of the Mississppi River