On September 17th, 1862, an army of the United States faced an army of the Confederate States near Antietam Creek in Sharpsburg, Maryland. This would be the day that would see the first battle of the American Civil War to be fought on Union soil. The Confederate Army of Northern Virginia, flush with confidence from their victory over the North at the Second Battle of Bull Run in August 1862, had crossed the Potomac into Maryland. A Confederate victory on enemy home territory, apart from its demoralizing impact, might increase European support for the South, as well as persuade Maryland to secede from the Union. At least that was part of the Confederate plan.
The Confederate Army of Northern Virginia, amounting to 38,000 men, was led by the inspirational, yet controversial, General Robert E. Lee. The force consisted of two large infantry corps, the First Corps led by Major General James Longstreet, and the Second Corps led by Thomas J. ‘Stonewall’ Jackson. Countering this invasion force was General George B. McClellan’s 75,300-man-strong Army of the Potomac, enhanced by units absorbed from John Pope’s Army of Virginia, and consisting of six infantry corps. Of these, the Ninth Corps, headed by Major-General Ambrose E. Burnside, was to play the most important role in the battle.
The battle began at dawn, with the powerful Union force's attempt to turn Lee’s left-flank. The attempt failed, and fighting broke out, spread all along a fractured front. Repeated Union attacks countered by equally ferocious Confederate counter-attacks swept like wildfire across Miller’s Cornfield and the West Woods. Later, a series of head-on attacks against Lee’s center bore fruit in terms of blood and life, but led to no decisive breakthrough. Late in the day, Burnside’s troops, crossing Burnside’s Bridge over Antietam Creek, managed to pierce the weakened line of Lee’s right flank, and only the timely arrival of reinforcements prevented Confederate defeat. Overall, McClelland’s cautious, piece-meal tactics failed to utilize his numerical superiority, allowing Lee to adapt to each new threat as they came.
The night of September 17th fell upon what had been the bloodiest single day in American military history. The Union side saw 2,100 soldiers killed, 9,950 wounded, with 750 missing or captured, comprising a total casualty count of 12,400. The Confederates suffered 1,550 deaths, with 7,750 wounded and 1,020 missing or captured, for a casualty total amounting to 10,320. Under cover of dark, both sides consolidated their positions and tended to their wounded, and neither side was able to claim an outright victory. The following day, however, Lee withdrew the Army of Northern Virginia back across the Potomac River, unhindered by the ever-cautious McClelland, leaving him the technical victor.
With combined casualties of 22,720 men, Antietam remains to be the single largest blood-stain upon the annals of American armed conflicts. But its significance spreads across the page into American and European political histories too. Despite a less than Napoleonic performance, McClelland was able to check the Confederate advance into the north. And, after a string of Union defeats, the general’s victory, albeit technical, emboldened Abraham Lincoln to make his Emancipation Proclamation which helped to decisively dissuade Britain and France from recognizing and aiding the Confederacy. Indeed, neither the British nor French public would have tolerated their government’s support for a slave-owning nation in a war against those wishing to emancipate their bondmen.