The Union assembled an army of 35,000 men (the largest ever seen in North America up to that point) under the command of General Irvin McDowell. With great fanfare, these untrained soldiers set out from Washington DC with the idea that they would capture Richmond in six weeks and put a quick end to the conflict. At the Battle of Bull Run on July 21, however, disaster ensued as McDowell's army was completely routed and fled back to the nation's capitol. Major General George McClellan of the Union was put in command of the Army of the Potomac following the battle on July 26, 1861. He began to reconstruct the shattered army and turn it into a real fighting force, as it became clear that there would be no quick, six-week resolution of the conflict. Despite pressure from the White House, McClellan did not move until March 1862, when the Peninsular Campaign began with the purpose of capturing the capitol of the Confederacy, Richmond, Virginia. It was initially successful, but in the final days of the campaign, McClellan faced strong opposition from Robert E. Lee, the new commander of the Army of Northern Virginia. From June 25 to July 1, in a series of battles known as the Seven Days Battles, Lee forced the Army of the Potomac to retreat. McClellan was recalled to Washington and a new army assembled under the command of John Pope.