By the end of the Maryland Campaign, both sides were worn out. From the end of June through September, 1862, the opposing armies fought some twenty engagements, in three campaigns, and inflicted more than 100,000 casualties combined. This pace was unsustainable and both sides took time to rest and refit.
President Lincoln removed General George B. McClellan from command on November 7, and his replacement, General Ambrose Burnside, quickly developed and implemented a new plan of operations. Burnside’s plan was inspired. He feinted toward Gordonsville to draw Lee away from his real goal, crossing the Rappahannock River at Fredericksburg, placing his army between Lee and Richmond. The Federals surprised Lee by covering 40 miles in two days. Upon reaching the Rappahannock, however, the plan fell apart. Burnside needed pontoons to cross the river, but the wagons carrying them failed to arrive. Heavy rains flooded the river and forced Burnside to wait for the pontoons. The delay gave Lee time to concentrate along the heights west of Fredericksburg.
Despite the strength of Lee’s defensive positions, Burnside crossed the Rappahannock on the late-arriving pontoons and occupied Fredericksburg on December 11. On December 13, he attacked Lee’s army. The Battle of Fredericksburg was a disaster for Federal forces. More than 12,000 Union soldiers became casualties without gaining any ground, while Lee suffered fewer than half as many. On December 15, Burnside retreated across the Rappahannock ending the active campaigning of 1862 in the Eastern Theater.