Battle of Antietam

On 17 September 1862, along Antietam Creek near the village of Sharpsburg, Maryland, the Union Army of the Potomac under George B. McClellan attacked Robert E. Lee's Confederate Army of Northern Virginia. The fighting cost the two sides about 22,700 men killed, wounded or missing, making it the bloodiest single day in American history. The battle itself ended in a draw, but Lee's retreat gave Abraham Lincoln the victory he needed to announce the Emancipation Proclamation, transforming the purpose of the American Civil War.

Fresh from victory at the Second Battle of Bull Run on 30 August, Lee led about 55,000 men into Maryland on 3 September. The Confederate leadership wanted to carry the war onto Union soil, Lee needed food that stripped northern Virginia could no longer supply, and many in the South assumed Maryland would welcome the invaders. Confederate leaders, including President Jefferson Davis, also thought a victory in the North might encourage Britain and France to recognise the Confederate States.

Lee divided his army, sending Stonewall Jackson to capture the Union garrison at Harpers Ferry, the town where John Brown's raid had taken place three years earlier. Then, by remarkable chance, two Union soldiers found a lost copy of Lee's orders wrapped around three cigars. McClellan now knew the enemy was scattered, but he waited about 18 hours before acting. Fighting at the passes of South Mountain delayed his advance long enough for Lee to gather much of his army at Sharpsburg.

The battle opened at dawn, when Joseph Hooker's corps struck Lee's left. For hours attacks and counter-attacks surged back and forth across a farmer's cornfield and around a small church of the Dunker sect. By the end of the morning the two sides had lost almost 13,000 men, and two Union corps commanders had been struck down.

The fighting then shifted to the Confederate centre, where troops held a farm lane worn deep into the ground. Union brigades attacked it repeatedly until a misunderstood order sent part of the Confederate line marching away and the defenders gave way, leaving the lane so full of bodies that it became known as Bloody Lane. Lee's centre was broken, but McClellan did not follow up the breakthrough.

To the south, Ambrose Burnside's corps spent much of the day trying to force its way across a narrow stone bridge over the creek, held by only about 400 Georgians. Once across, his men pushed towards Sharpsburg and threatened to cut Lee off from the Potomac. At the critical moment, A. P. Hill's division arrived after a hard march from Harpers Ferry and struck Burnside's flank, driving the Federals back. The fighting was over by about 5:30 p.m.

Lee, outnumbered roughly two to one, had committed every unit he had, while McClellan used less than three-quarters of his army. Union losses were about 12,400, Confederate losses about 10,300, with roughly 3,650 killed outright on the two sides combined. Several generals on each side were killed or mortally wounded. After an informal truce on 18 September to recover the wounded, Lee withdrew into Virginia. Photographs of the dead taken by Alexander Gardner and James Gibson shocked the Northern public; never before had an American battlefield been photographed while the dead still lay on it.

Lincoln was frustrated that McClellan did not pursue Lee, and in November he removed him from command. Yet the battle ended Lee's first invasion of the North, and on 22 September Lincoln issued the preliminary Emancipation Proclamation, warning that enslaved people in states still in rebellion on 1 January 1863 would be declared free. By tying the Union cause to the end of slavery, the proclamation made it much harder for Britain or France, both of which had already abolished slavery, to recognise or aid the Confederacy.

The war fell between our map years: the 1815 map shows Maryland within the United States, and the 1878 map shows the country reunited after the war.