Jackson taking over railway for Union supplies and communication was key.
This was the culmination of an offensive campaign waged by Confederate Gen. Robert E. Lee and a battle of much larger scale and numbers than the First Battle of Full Run that was 14 months earlier.
Following a wide-ranging flanking march, Confederate Maj. Gen. Thomas J. "Stonewall" Jackson captured the Union supply depot at Manassas Junction, threatening Pope's line of communications with Washington, D.C.
On August 28, 1862, Jackson (Confederate) attacked a Union column just east of Gainesville, at Brawner's Farm, resulting in a stalemate. That same day, the wing of Lee's army commanded by Maj. Gen. James Longstreet broke through light Union resistance in the Battle of Thoroughfare Gap and approached the battlefield.
Pope (Union) became convinced that he had trapped Jackson and concentrated the bulk of his army against him. On August 29, Pope launched a series of assaults against Jackson's position along an unfinished railroad grade. The attacks were repulsed with heavy casualties on both sides. At noon, Longstreet (Confederate) arrived on the field from Thoroughfare Gap and took position on Jackson's right flank.
When massed Confederate artillery devastated a Union assault by Maj. Gen. Fitz John Porter's V Corps, Longstreet's wing of 25,000 men in five divisions counterattacked in the largest, simultaneous mass assault of the war. The Union left flank was crushed and the army was driven back to Bull Run.
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