After Antietam, Lincoln had had enough of McClellan.  Rather than push the attack a second day or pursue the retreating Lee, McClellan had chosen his customary caution. Lincoln, therefore, fired McClellan and replaced him with Ambrose Burnside.  

If McClellan had been frustratingly cautious, Burnside would prove catastrophically rash.  He believed that if he feigned an attack in Northern Virginia then rapidly marched south toward Richmond via Fredericksburg, he could catch Confederate General Robert E. Lee napping.   Yeah, right.

Lincoln sensed that Burnside underestimated Lee; the plan would only succeed if the thus-far error proof Lee did bite on Burnside’s fake and Burnside did move with unflagging speed.  But neither occurred.  Burnside reached Fredericksburg on 15 November and prepared to cross the Rappahannock River—but the pontoon bridges he expected to find there had not arrived. Burnside debated his options and, ultimately, pulled a McClellan—he decided to wait.  By the time his pontoon bridges arrived and he had moved his men across the river, Lee, Stonewall Jackson, and James Longstreet, the defensive wizard, had all reached Fredericksburg and prepared elaborate defenses.

Despite the fact that Burnside enjoyed neither the element of surprise nor the tactical advantage he had wanted, he decided to press ahead.  Covering artillery fire allowed him to transport a large part of his force across the river on December 11 and 12.  Once in Fredericksburg, the Union troops looted the town with abandon—providing Lee and his men with unneeded incentive to unload on the offending troops.

On the thirteenth, Burnside ordered his men into battle. The first attacks were launched against well-entrenched forces commanded by Stonewall Jackson on the right side of the Confederate lines.  When these failed, Burnside shifted the attack to equally well-entrenched forces under Longstreet on the Confederate left. This assault proved particularly costly. Longstreet’s men were positioned in a sunken road given further protection by a rock wall.  They picked off the advancing Yankees like fish in a barrel.  Yet Burnside continued to press the attack.  By the end of the day, the general had ordered fourteen different assaults, none of them successful and all of them terribly costly.

Burnside lost almost 11,000 men in his injudicious attacks—1284 killed, 9600 wounded.  Lee lost less than half that number. Burnside also lost his job.  Lincoln replaced the bungling Burnside with General Joseph Hooker.