September 17, 1862, climaxed the first of Confederate Gen. Robert E. Lee's two attempts to carry the war into the North. About 40,000 Southerners were pitted against the 85,000-man Federal Army of the Potomac under Gen. George B. McClellan. And when the fighting ended, the course of the American Civil War had been greatly altered.
After his great victory at Manassas in August, Lee had marched his Army of Northern Virginia into Maryland, hoping to find vitally needed men and supplies. McClellan followed, first to Frederick (where through rare good fortune a copy of the Confederate battle plan, Lee's Special Order No. 191, fell into his hands), then westward 12 miles to the passes of South Mountain. There on September 14, at Turners, Fox, and Cramptons Gaps, Lee tried to block the Federals. Because he had split his army to send troops under Sen. Thomas J. "Stonewall" Jackson to capture Harpers Ferry, Lee could only hope to delay the Northerners. McClellan forced his way through, and by the afternoon of September 15 both armies had established new battle lines west and east of Antietam Creek near the town of Sharpsburg. When Jackson's troops reached Sharpsburg on the 16th, Harpers Ferry having surrendered the day before, Lee consolidated his position along the low ridge that runs north and south of the town.
The battle opened at dawn on the 17th when Union Gen. Joseph Hooker's artillery began a murderous fire on Jackson's men in the Miller cornfield north of town. "In the time I am writing," Hooker reported, "every stalk of corn in the northern and greater part of the field was cut as closely as could have been done with a knife, and the slain lay in rows precisely as they had stood in their ranks a few moments before." Hooker's troops advanced, driving the Confederates before them, and Jackson reported that his men were "exposed for near an hour to a terrific storm of shell, canister, and musketry."
About 7 a.m. Jackson was reinforced and succeeded in driving the Federals back. An hour later Union troops under Gen. Joseph Mansfield counterattacked and by 9 o'clock had regained some of the lost ground. Then, in an effort to extricate some of Mansfield's men from their isolated position near the Dunker Church, Gen. John Sedgwick's division of Edwin V. Sumner's corps advanced into the West Woods. There Confederate troops struck Sedgwick's men on both flanks, inflicting appalling casualties.
Meanwhile, Gen. William H. French's division of Sumner's corps moved up to support Sedgwick but veered south into Confederates under Gen. D. H. Hill posted along an old sunken road separating the Roulette and Piper farms. For nearly 4 hours, from 9:30 a.m. to 1 p.m., bitter fighting raged along this road (afterwards known as Bloody Lane) as French, supported by Gen. Israel B. Richardson's division, also of Sumner's corps, sought to drive the southerners back. Confusion and sheer exhaustion finally ended the battle here and in the northern part of the field generally.
Gen. Ambrose Burnside's troops had been trying to cross a bridge over Antietam Creek since 9:30 a.m. Some 500 Georgians had driven them back each time. At 1 p.m. the Federals finally crossed the bridge (now known as Burnside Bridge) and, after a 2-hour delay to reform their lines, advanced up the slope beyond. By late afternoon, they had driven the Confederates back almost to Sharpsburg, threatening to cut off the line of retreat for Lee's decimated army. Then about 4 p.m. Gen. A. P. Hill's division, left behind by Jackson at Harpers Ferry to salvage the captured Federal property, arrived on the field and immediately entered the fight. Burnside's troops were driven back to the heights near the bridge they had earlier taken. The Battle of Antietam was over. The next day Lee began withdrawing his army across the Potomac River.
It has been said that more men were killed or wounded at Antietam on September 17, 1862, than on any other single day of the Civil War. Federal losses were 12,410, Confederate losses 10,700. Although neither side gained a decisive victory, Lee's failure to carry the war effort effectively into the North caused Great Britain to postpone recognition of the Confederate government. The battle also gave President Abraham Lincoln the opportunity to issue the Emancipation Proclamation, which, on January 1, 1863, declared free all slaves in States still in rebellion against the United States. Now the war had a dual purpose: to preserve the Union and end slavery.