Jefferson Davis appointed Robert E. Lee commander of the Army of Northern Virginia in June 1862 after General Joseph E. Johnston was injured during fighting in the Peninsular Campaign.Lee attacked McClellan's army three weeks later and in savage fighting during the Seven Days' Campaign forced the Union army out of the Peninsula. That saved Richmond for the time being.As the war wore on Lee realized he needed to change his strategy. Rather than keep fighting McClellan in Virginia he decided to bring the fighting closer to Washington, so he shifted his campaign to Maryland. The Army of Northern Virginia marched into Maryland on September 4th, 1862. Once inside Maryland, Lee divided his army of 55,000 men into four parts. General James Longstreet marched to Boonsboro then Hagerstown, Stonewall Jackson to Harper's Ferry to capture the government arsenal there, and D. H. Hill and JEB Stuart stood guard in the rear at South Mountain. Unfortunately for Lee, Corporal Barton Mitchell of the 27th Indiana Infantry discovered a lost copy of his Special Order 191 on September 13. It gave McClellan a blueprint showing all the movements for the Army of Northern Virginia during the Maryland campaign.For the over-cautious McClellan, the paper appeared to be a Godsend. He quickened his pace and met Lee at South Mountain the next day. Unfortunately, McClellan settled for a partial victory. That set Stonewall Jackson up for his victory at Harper's Ferry and allowed the rest of Lee's army to escape to Sharpsburg where he would soon have another showdown with General George McClellan and his Army of the Potomac.September 17th, 1862 would be the bloodiest day of fighting during the civil war with over 23,000 men reported killed, missing, and wounded on both sides.Antietam: The Bloodiest Day outlines the battle and explains how it came about. In less than an hour, you will meet the main participants, understand Union and Confederate troop movements, and learn why Abraham Lincoln thought McClellan's great victory was a lost opportunity. For those readers who want to know more and understand how contemporary readers learned about the battle, we included the original accounts printed in the New York Herald and the New York Tribune.