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Battle of Antietam
September 17, 1862· Battle· Americas
Well documentedSolid records, physical evidence or scientific consensus.
McClellan's Union army stopped Robert E. Lee's invasion of Maryland in a single day of fighting near Sharpsburg.
See it on the Battles & Wars map →What happened
Union soldiers found a lost copy of Lee's orders, showing his army was divided. George McClellan's army, about 75,000–87,000 men by most estimates, attacked Lee's 38,000–45,000 along Antietam Creek. Fighting moved from the Cornfield in the morning to the Sunken Road, later called 'Bloody Lane', to a stone bridge in the afternoon. Confederate reinforcements arrived just in time. McClellan held reserves back and did not renew the attack; Lee withdrew to Virginia. About 23,000 men were killed, wounded or missing.
Why it matters
The Union could claim a victory, so five days later Lincoln announced the Emancipation Proclamation. That made ending slavery a war aim and helped keep Britain and France from intervening.
How we know
Reports in the Official Records, soldiers' letters, the preserved Antietam National Battlefield, and Alexander Gardner's photographs of the dead, shown in New York weeks later.
Still debated
Why McClellan was so cautious despite knowing Lee's plans, and how the Confederate order came to be lost, wrapped around three cigars, remain debated.
Connections (3)
▸Battle of Antietam was the bloodiest single day of American Civil WarWell documented
The connection
About 23,000 men were killed, wounded or missing in roughly twelve hours, including some 3,600 killed outright, more Americans than on any other single day of war. Its political result mattered even more: it gave Lincoln the victory he wanted before announcing emancipation, changing the war's purpose.
When and how
Sharpsburg, Maryland, September 17, 1862; McClellan's Army of the Potomac against Lee's Army of Northern Virginia.
How we know
Casualty returns compiled by both armies in the Official Records; the National Park Service uses about 23,000 total casualties.
Debates and open questions
Exact totals differ between sources, and many wounded died later, so the true death toll is uncertain.
▸Robert E. Lee was halted in Maryland at Battle of AntietamWell documented
The connection
After winning at Second Bull Run, Lee invaded Maryland in September 1862, hoping for recruits, supplies and foreign recognition. He split his army to capture Harpers Ferry. When McClellan advanced, Lee chose to stand at Sharpsburg with the Potomac River behind him. He held off repeated attacks, then retreated to Virginia.
When and how
Maryland Campaign, September 4–20, 1862; Lee's Army of Northern Virginia at Sharpsburg, with Stonewall Jackson's troops arriving from Harpers Ferry.
How we know
Lee's own orders and reports, including the lost Special Order 191, survive in the Official Records; the campaign is thoroughly documented.
Debates and open questions
Why Lee risked battle with a much smaller army and a river at his back, rather than retreating at once, is still debated.
▸Battle of Antietam ended Lee's first northern invasion, before Battle of GettysburgWell documented
The connection
Antietam turned back Lee's first invasion of the North. After victories at Fredericksburg and Chancellorsville he tried again in summer 1863, reaching Pennsylvania, and was defeated at Gettysburg. Both campaigns aimed at Northern war-weariness and foreign support, and after both, Lincoln criticized his commander for letting Lee escape across the Potomac.
When and how
Maryland, September 1862, and Pennsylvania, July 1863; Lee against McClellan, then against George Meade.
How we know
Both campaigns are fully documented in the Official Records and Lincoln's letters; the comparison is standard among historians.
Debates and open questions
Whether Lee's invasions were sound strategy, or wasted men the Confederacy could not replace, is one of the war's long-running debates.