In July, 1862, General John Pope, commander of the Army of Virginia, decided to try a capture Gordonsville, a railroad junction between Richmond and the Shenandoah Valley. Pope selected Nathaniel Banks to carry out the task. Robert E. Lee considered Gordonsville to be strategically very important and sent Thomas Stonewall Jackson to protect the town. On 9th August, Jackson defeated Banks at Cedar Run. Pope now ordered George McClellan army based at Harrison's Landing to join the campaign to take the railroad junction. When Lee heard this news he brought together all the troops he had available to Gordonsville.
On 29th August, troops led by Thomas Stonewall Jackson and James Longstreet, attacked Pope's Union Army at Manassas, close to where the first battle of Bull Run had been fought. Pope and his army was forced to retreat across Bull Run. The Confederate Army pursued the Army of Virginia until they reached Chantilly on 1st September.
The Union Army lost 15,000 men at Bull Run. General John Pope was blamed for the defeat. A staff officer later recalled that "Pope was entirely deceived and outgeneralled. His own conceit and pride of opinion led him into these mistakes." Relieved of his command Pope was sent to Minnesota to deal with a Sioux uprising.
I have come to you from the West, where we have always seen the backs of our enemies; from an army whose business it has been to seek the adversary, and to beat him where he was found; whose policy has been attack and not defense. I presume that I have been called here to pursue the same system and to lead you against the enemy. It is my purpose to do so, and that speedily. Meantime I desire you to dismiss from your minds certain phrases which I am sorry to find so in vogue amongst you. I hear constantly of "taking strong positions and holding them", of "lines of retreat", and of "bases of supplies". Let us discard such ideas.
Our surgeons began to prepare for the coming battle, by appropriating several buildings and fitting them up for the wounded - among others the stone church at Centreville - a church which many a soldier will remember, as long as memory lasts.
The first man I saw killed was a gunner. A shell had burst in the midst of the battery, killing one and wounding three men and two horses. Now the battle began to rage with terrible fury. Nothing could be heard save the thunder of artillery, the clash of steel, and the continuous roar of musketry.
I was sent off to Centreville, a distance of seven miles, for a fresh supply of brandy, lint, etc. When I returned, the field was literally strewn with wounded, dead and dying. Men tossing their arms wildly calling for help; there they lie bleeding, torn and mangled; legs, arms and bodies are crushed and broken as if smitten by thunderbolts; the ground is crimson with blood.
Stonewall Jackson, with a force of 26,000 men, had worked his way through Thoroughfare Gap to the north of us, had swooped all around Pope's flank, having made a march of fifty miles in thirty-six hours and pounced upon Manassas Junction, where Pope's supplies and ammunition were stored, helping himself to whatever he could use and carry off, and burning the rest. Jeb Stuart's troopers, accompanying Jackson, had even raided Pope's headquarters at Catlett's Station. It was a brilliant stroke, but at the same time most hazardous, for Pope's largely superior forces might have been rapidly concentrated against him, with Longstreet, his only support, still far away.
Pope was entirely deceived and outgeneralled. His own conceit and pride of opinion led him into these mistakes. On the field his conduct was cool, gallant, and prompt.