The Army of Northern Virginia was not destroyed after the battle of Antietam due to the lack of aggression by the Union commander, George McClellan. Abraham Lincoln replaced him with Ambrose Burnside, hoping that Burnside would be more aggressive. The result was the Army of the Potomac's greatest, and most tragic, defeat at Fredericksburg, Virginia, on December 12 and 13, 1862.
For a history of the Fredericksburg campaign, click here.
Click on the picture on the map, or on the link below the map, to see photographs from that portion of the battlefield.