The memory of the Battle of Antietam was so haunting that when, nine months later, Major Rufus Dawes learned another Antietam battle might be on the horizon, he wrote, "I hope not, I dread the thought of the place." In this definitive account, historian D. Scott Hartwig chronicles the single bloodiest day in American history, which resulted in 23,000 casualties.The Battle of Antietam marked a vital turning point in the war: afterward, the conflict could no longer be understood as a limited war to preserve the Union, but was now clearly a conflict over slavery. Though the battle was tactically inconclusive, Robert E. Lee withdrew first from the battlefield, thus handing President Lincoln the political ammunition necessary to issue the Emancipation Proclamation.Based on decades of research, this in-depth narrative sheds particular light on the visceral experience of battle, an often misunderstood aspect of the American Civil War, and the emotional aftermath for those who survived. Hartwig provides an hour-by-hour tactical history of the battle, beginning before dawn on September 17 and concluding with the immediate aftermath, including General McClellan's fateful decision not to pursue Lee's retreating forces back across the Potomac to Virginia.