sep 17, 1862 - The Battle of Antietam takes place, the bloodiest day in American history at the time

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After pursuing the Confederate general Robert E. Lee into Maryland, Maj. Gen. George B. McClellan of the Union Army launched attacks against Lee's army, in defensive positions behind Antietam Creek. At dawn on September 17, Maj. Gen. Joseph Hooker's corps mounted a powerful assault on Lee's left flank. Attacks and counterattacks swept across Miller's Cornfield, and fighting swirled around the Dunker Church. Union assaults against the Sunken Road eventually pierced the Confederate center, but the Federal advantage was not followed up. In the afternoon, Union Maj. Gen. Ambrose Burnside's corps entered the action, capturing a stone bridge over Antietam Creek and advancing against the Confederate right. At a crucial moment, Confederate Maj. Gen. A. P. Hill's division arrived from Harpers Ferry and launched a surprise counterattack, driving back Burnside and ending the battle. Although outnumbered two-to-one, Lee committed his entire force, while McClellan sent in less than three-quarters of his army, enabling Lee to fight the Federals to a standstill. During the night, both armies consolidated their lines. In spite of crippling casualties, Lee continued to skirmish with McClellan throughout September 18, while removing his battered army south of the Potomac River. Due to the belief that he was outnumbered McClellan continued to be overcautious and Lee's army was aloud to escape. While he did halt the invasion, McClellan's refusal to pursue the retreating army led to his removal from command by President Lincoln. With a combined tally of almost 23,000 dead wounded or missing, it was the bloodiest battle in America at the time, until it was outdone just under a year later.

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