After Robert E. Lee's new command, the Army of Northern Virginia, defeated George B. McClellan's vastly superior Army of the Potomac in the Peninsular Campaign, Union high command in Washington D. C. decided to move McClellan's army by sea back to northern Virginia, where it would be united with a force of about 50,000 men left over from the Valley Campaign already there. The man who was placed in command of these troops was John Pope. Pope was extremely overconfident and bombastic, and he was hated by many of the troops and generals. He had once (supposedly) said that his headquarters were "in the saddle", which resulted in a joke being circulated that "his headquarters are where his hindquarters should be." Once these forces were combined, they would then march overland to capture Richmond, the Confederate capital.
Lee, with an army of about 55,000 men, knew he was greatly outnumbered. He seized the opportunity to attempt to destroy Pope's forces before they were joined by McClellan. He sent Stonewall Jackson's corps of 25,000 "foot cavalry" (the nickname of Jackson's men in the Valley Campaign) marching into Pope's rear, where they captured a supply dump. Pope followed Jackson and the two forces met near the railroad junction of Manassas, the site of the first major battle of the civil war (First Manassas), a year earlier. Pope decided to use his numerical superiority to crush Jackson before any reinforcements arrived. On August 29, 1862, around mid-day, Pope began launching piecemeal attacks on Jackson's men, entrenched on an elevated unfinished railroad bed.
Throughout the whole day, Pope's troops launched uncoordinated assaults on the railroad. As night fell, both sides had suffered many casualties. Once, a defending group of Confederates ran out of ammunition and held off the Federals by throwing rocks collected from the railroad bed. Pope planned to renew the attack at dawn the next day. He seemingly did not know about James Longstreet's corps of 28,000 men placed on the Federal left flank. On August 30, Pope continued his assaults on Jackson's men. Longstreet withheld his men until he felt that Pope had substantially weakened himself, and, at about 4:00 P. M. on August 30, Longstreet's corps surged forward in what became the largest simultaneous coordinated assault of the war. Pope's uncovered left flank was repeatedly enfiladed (hit by fire from the side) by Confederate artillery and attacked. Then, Jackson's defending corps suddenly jumped from defense to offense. Pope's men panicked, and where driven before Longstreet. The men were then marched all the way to Washington D. C., where Pope was relieved of his command.
This battle of Second Manassas (alternately, Second Bull Run) cost the Confederates 9,000 casualties and cost the Union 14,000. Lee claimed to have captured 7,000 prisoners and 30 guns (pieces of artillery, not muskets, which are worth far less.) However, Pope claimed to have lost no guns at all. Lee's report of capturing the guns turned out to be the more correct one, but the prisoner report still hasn't been confirmed. The bottom line: Lee won the battle, and then marched his army into Maryland in his first invasion of the north, which culminated in the stalemate at Antietam.
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