ORDER OF BATTLE // September 20, 1862
Maryland Campaign
Estimated force strength by side, with confidence labels per surviving record.
Forces engaged
2 sides catalogued · combined 157,234 estimated
United States
102,234
Medium-confidence figure
Confederate States
55,000
Medium-confidence figure
Battle context
The Maryland Campaign of September 1862 marked Confederate General Robert E. Lee's first invasion of Union territory. Lee moved his Army of Northern Virginia north across the Potomac, prompting Maj. Gen. George B. McClellan to advance with the Army of the Potomac to intercept him. The campaign culminated in fighting near Sharpsburg, Maryland, in what became the bloodiest single day of battle in American history. McClellan succeeded in repulsing the invasion, preventing Lee from establishing a Confederate presence on Union soil. Union forces outnumbered the Confederate army by a substantial margin, though both sides suffered heavy casualties — together exceeding 44,000 men. The repulse of Lee's first northern invasion carried significant strategic weight, denying the Confederacy the kind of decisive offensive success that might have influenced foreign recognition or altered the broader momentum of the war.
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