The correct answer is D, as the Second Battle of Bull Run placed Washington DC in danger.
The Second Battle of Bull Run took place between August 28 and August 30, 1862, during the Northern Virginia Campaign of the American Civil War.
It was the culmination of an offensive campaign waged by the Northern Virginia Army of Confederate General Robert E. Lee against the Virginia Army of Unionist General John Pope. It was a battle on a much larger scale than the first battle of Bull Run, both fought in the same area. The outcome of the battle was a Confederate victory, but the Union Army remained largely intact.
After a broad flanking move, Confederate General Thomas J. "Stonewall" Jackson captured the Union's supply depots in Manassas Junction on Aug. 27, threatening Pope's Army communication line with the city of Washington. After his raid, Jackson retreated to the northwest, taking defensive positions at Stony Ridge and waiting for the rest of the Confederate troops. On August 28, Jackson attacked a Union column east of Gainesville, on Brawner's Farm, with no favorable outcome for either side. That same day, Lee's wing commanded by Maj. Gen. James Longstreet broke the weak federal resistance it encountered in the Thoroughfare Gap and approached Jackson's troops.
The Union had about 10,000 dead and wounded of the 62,000 involved in the battle; The Confederacy had about 1,300 dead and about 7,000 injured of approximately 50,000 who fought. While the Union army was concentrated in Centerville, Lee planned his new move. He sent Jackson to conduct another flanking march with the intention of interposing himself between Pope's army and Washington, which had been left almost unprotected after the battle. Pope responded to this movement and the two forces clashed at the Battle of Chantilly on September 1.
