On August 29, Union troops led by using John Pope struck Jackson’s forces within the 2nd war of Bull Run (2d Manassas). the next day, Lee hit the Federal left flank with a huge assault, riding Pope’s men back in the direction of Washington. at the heels of his victory at Manassas, Lee started out the primary confederate invasion of the North. no matter contradictory orders from Lincoln and Halleck, McClellan was able to reorganize his military and strike at Lee on September 14 in Maryland, using the Confederates returned to a shielding function along Antietam Creek, close to Sharpsburg. On September 17, the military of the Potomac hit Lee’s forces (strengthened via Jackson’s) in what became the battle’s bloodiest single day of preventing. general casualties at Antietam numbered 12,410 of some 69,000 troops at the Union facet, and 13,724 of around 52,000 for the Confederates. The Union victory at Antietam might prove decisive, as it halted the confederate improve in Maryland and forced Lee to retreat into Virginia. still, McClellan’s failure to pursue his gain earned him the scorn of Lincoln and Halleck, who eliminated him from command in favor of Ambrose E. Burnside. Burnside’s attack on Lee’s troops close to Fredericksburg on December thirteen ended in heavy Union casualties and a confederate victory; he was directly changed by means of Joseph “fighting Joe” Hooker, and both armies settled into wintry weather quarters across the Rappahannock River from everyother.