As Union commander George McClellan moved the Army of the Potomac up the Peninsula in early 1862, the Union army had a nearly 2-1 advantage in manpower, so Army of Northern Virginia commander Joseph E. Johnston continued to gradually pull his troops back to a line of defense nearer Richmond as McClellan advanced. In conjunction, the Union Navy began moving its operations further up the James River, until it could get within 7 miles of the Confederate capital before being opposed by a Southern fort. It was at this point that Johnston got uncharacteristically aggressive at the end of May, perhaps because he had run out of breathing space for his army. By the time the Battle of Seven Pines was over, nearly 40,000 had been engaged on both sides, making it the biggest battle in the Eastern theater to date, and Johnston was injured, bringing Robert E. Lee to command.Despite not losing, the fighting rattled McClellan, but even after Lee pushed McClellan's Army of the Potomac away from Richmond and back up the Peninsula in late June, he then had to swing his army north to face a second Union army: John Pope's Army of Virginia. Correctly assuming that he needed to strike out before the Army of the Potomac successfully sailed back to Washington and linked up with Pope's army, Lee daringly split his army to threaten Pope's supply lines, forcing Pope to fall back to Manassas to protect his flank and maintain his lines of communication. At the same time, it left half of Lee's army (under Stonewall Jackson) potentially exposed against the larger Union army until the other wing (under James Longstreet) linked back up. Thus, in late August 1862, the Army of Northern Virginia and the Army of Virginia found themselves fighting over nearly the exact same land the North and South fought over in the First Battle of Bull Run 13 months earlier.