Battle Of Antietam: The Second Deadliest Day In American History

By | December 13, 2020

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"The Battle of Antietam - Army of the Potomac, General George B. McClellan, commander, September 17, 1862," color lithograph, unknown artist, 1888, published by Kurz & Allison, Art Publishers, Chicago. (VCG Wilson/Corbis via Getty Images)

When 3,650 people died on September 17, 1862, it became the single deadliest day in American military history and the second deadliest day the country has ever seen at all, just behind the Galveston hurricane of 1900. The Battle of Antietam, also called the Battle of Sharpsburg, turned the tide of the American Civil War, in part due to the staggering number of casualties and in part thanks to the new technology of photography that brought the horrors of the battlefield to newspapers across the country. While the Battle of Antietam was a key moment in the Civil War, it was also an event filled with missed opportunities.

Both Sides Needed The Win

The Union Army assumed that victory over the Confederacy would be swift and easy, but as summer 1862 wore on, it became clear that the Southern states were a formidable foe. The Confederacy hammered this home with their defeat of Major General John Pope and the Union troops at the Second Battle of Bull Run. President Abraham Lincoln had his Emancipation Proclamation ready to announce, but he knew it would carry much more weight if it came on the heels of a decisive Union victory.

To make matters worse, Lincoln was facing a mid-term election that threatened to flip control of Congress from Lincoln's Republicans to the anti-war Democrats. Confederate General Robert E. Lee was well aware of this, of course, and hoped a few more Union defeats might swing the mid-term election to the Democrats, thus yanking Lincoln's congressional support.

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Abraham Lincoln and George B. McClellan in the general's tent at Antietam, Maryland, October 3, 1862. (Library of Congress/Wikimedia Commons)

General George B. McClellan, a Questionable Leader

The Battle of Antietam was all important for Union General George B. McClellan, who had planned to attack the Confederate capital of Richmond, Virginia the previous summer only to be derailed by a counterattack from Lee. Sensing an opportunity to kick the Union army while they were down, Lee moved his troops north into Maryland and took over the town of Frederick, where he laid out his plans to push his forces into Northern territory and split his army in two to take Hagerstown, Maryland and Martinsburg, West Virginia. He called his plan Special Order 191.

As Lee's men marched out of their camp in Frederick, however, someone made a critical mistake. General McClellan's army happened upon the abandoned Confederate camp, and Sergeant John M. Bloss and Private Barton W. Mitchell discovered three cigars loosely wrapped in a sheet of paper lying on the ground. Likely hoping for nothing more than a good smoke, they soon realized the paper contained Special Order 191. An ecstatic McClellan immediately began strategizing to thwart Lee's battle plans, but at the same time, Lee discovered his plans were missing and hurried to reunite his forces.