American Civil War battle that ended Robert E. Lee’s first invasion of the north. After victory at Second Bull Run or Manassas (29-30 August), Lee was convinced that the best chance of Confederate victory was an invasion of the north. At best, a major Confederate victory on northern soil might convince foreign governments to recognise the independence of the south, and perhaps persuade Maryland to join the rebels, a step that might even result in the capture of Washington.
However, Lee’s move north was very poorly handled. At this point he seems to have held the Union army, and its commanders, almost in contempt. In order to capture Harpers Ferry, he split his army into five segments, on the assumption that by the time news of this reached Union ears, his army would be back together again.
This was improbable to say the least. McClellan was receiving a great deal of accurate intelligence about Lee’s movements now he was in Maryland, but on 13 September he received a stroke of luck that should have allowed him to roll up Lee’s entire army. A copy of Lee’s Special Order 191, detailing his plan for the attack on Harpers Ferry, was found by two Union solders. Worse, the copy was written in handwriting that was recognised as belonging to Lee’s assistant adjutant-general. The order was genuine, and McClellan accepted it as such.
Even with this information, McClellan still proved incapable of moving quickly. On 14 September he managed to force his way through the mountain passes north of Harpers Ferry, but then halted again. Harpers Ferry did not fall to the Confederates until the following day, 15 September. On that same day, Lee decided to move his part of the army, some 15,000 men, south to Sharpsburg, with Antietam Creek running south to north just to his east. The first Federal units reached the east bank of the creek at noon on the same day.
This was McClellan’s great chance. The bulk of his army was no more than half a days march away. On 15 September he could have attacked Lee’s 15,000-20,000 men with most of his 80,000. The following day part of the Harpers Ferry force reached Lee, but even at the end of the day he only had 25,000 men. Still McClellan did not attack.
Finally, on 17 September McClellan attacked. The resulting Battle of Antietam or Sharpsburg saw a series of determined but uncoordinated Union attacks that came close to breaking Lee’s line on several occasions. On each occasion, McClellan failed to support the attack, and convinced that he was still outnumbered never used his reserves. Antietam saw the highest casualty figures of any single days fighting in the entire war. Lee lost 2,700 dead, 9,024 wounded and 2,000 missing out of a total force of 40,000. Union losses were 2,108 killed, 9,549 wound and 753 missing out, similar total numbers out of a much larger army.
McClellan was given yet another chance on 18 September. Lee remained in his lines all day, with his forces down to at most 30,000 men. McClellan had nearly that many fresh soldiers who had taken no part in the fighting on the previous day, but was still convinced that Lee had massive reserves, and did not attack. Finally, during the evening of 18 September Lee withdrew across the Potomac back into Virginia.
Antietam was McClellan’s last great chance to defeat Lee. On 7 November he was finally replaced as commander of the Army of the Potomac. He persisted in claiming Antietam as a military masterpiece. Although it was far from that, it did have long reaching effects. For some time Lincoln had been waiting for a victory before issuing the Emancipation Proclamation. Antietam was enough of a victory. The Proclamation helped change the nature of the war, giving the Union cause a great moral advantage. Antietam also discouraged any thoughts the British government might have had about recognising the Confederacy. Lee’s gamble had failed.