Antietam Was the Bloodiest Day in American History and It Changed the War

A cornfield, a sunken country lane and a stone bridge over a creek that a man could have waded in many places. Three ordinary pieces of Maryland farmland, and on a single day in September 1862 they became names that Americans learned to say with lowered voices.

If you want to understand what the Civil War cost, begin at Antietam. If you want to understand how a war changes its own purpose, begin there too. Because the battle did two things at once: it stopped the Confederate invasion of the North, and it handed Abraham Lincoln the thing he had been waiting for, a victory large enough to stand on while he announced that the war would now be fought to end slavery. The casualties were awful, the generalship was uneven, and the political consequences changed the country.

The road to Sharpsburg

The summer of 1862 had been bad for the Union. George McClellan's army had come within sight of Richmond on the Peninsula, and Robert E. Lee, newly in command of the Confederate Army of Northern Virginia, had driven it back in the Seven Days. At the end of August, Lee smashed John Pope's army at the Second Battle of Bull Run. Washington was exposed, and the Union's morale was low.

Lee decided to cross the Potomac and take the war into the North. He had reasons. Maryland was a slave state and he hoped for recruits. A victory on Northern soil might swing the November elections toward the peace party, and might persuade Britain and France, both of whom were weighing whether to recognize the Confederacy, to act. And his army needed to live off the countryside, which Virginia's farms, devastated by two years of war, could no longer supply. In early September, the Army of Northern Virginia crossed into Maryland, the first invasion of the North by the army that would, the next summer, try again at Gettysburg, a battle we cover in Gettysburg in Three Days and the Charge That Failed on July 3, 1863.

Lee then took a risk that may have been the most consequential gamble of the campaign. He divided his army. He sent Stonewall Jackson with a large part of it to capture the Union garrison and arsenal at Harpers Ferry, which sat behind him and threatened his supply line, while the rest of the army moved north and west. The plan, which a careful general commits to paper and a careless officer commits to his pocket, was written in an order, known as Special Order 191, which laid out the movements of each column.

The lost order

On September 13, 1862, Union soldiers resting in a field near Frederick, Maryland, found a piece of paper wrapped around three cigars. It was a copy of Lee's Special Order 191, dropped by a Confederate officer. A corporal of an Indiana regiment found it, and it went up the chain of command to McClellan within hours. McClellan knew then that Lee's army was split, with its parts several miles apart.

You would think a general with Lee's plan in his pocket would have moved at once. McClellan moved, but not fast, in the manner of a man who has been handed the answer key and wants to check it twice before writing anything down. Historians have debated for 160 years how much time he lost, and the fairest answer is that he lost the chance to destroy Lee's divided army piece by piece. He did force the passes of South Mountain on September 14, in a bitter fight, and the Confederates fell back toward Sharpsburg, a small town near the Potomac, with Antietam Creek running along its east side. On September 15 Jackson captured Harpers Ferry and its garrison of about twelve thousand Union soldiers, a major embarrassment for the Union, and then marched hard to rejoin Lee.

Lee, with the Potomac at his back and his army still reassembling, chose to stand and fight. It was an audacious decision, and some of his own officers thought it reckless. Lee had well under forty thousand men on the field, and McClellan had more than seventy thousand available to him.

The morning: the Cornfield

The battle opened at dawn on September 17 with a Union attack on the Confederate left, north of Sharpsburg, by Joseph Hooker's corps. The ground in front of them was a field of tall corn, owned by a farmer named David Miller. Confederate infantry and artillery were waiting in and beyond the corn.

What followed in the Cornfield was a fight of terrible intensity. The cornfield changed hands several times in the first hours. Union and Confederate lines swept back and forth across it in succession, each assault stopped by close-range fire. Units from both sides were nearly destroyed. By midmorning the Cornfield was covered with dead and wounded. John Bell Hood's division, with its Texas regiments, was brought up to counterattack and suffered a staggering loss. Hooker himself was wounded and taken from the field.

The fighting then moved to the West Woods and to the center, where Union attacks came in piecemeal because of poor coordination. McClellan, behind the lines, was directing a battle by messengers, and his corps commanders were attacking one at a time, not together. That lack of coordination is the first thing a military student notes about Antietam. If all the Union attacks had gone in together, the Confederate line might have broken.

Midday: the Sunken Road

At the center of the Confederate line was a worn country lane, sunk below the level of the surrounding fields by years of wagon traffic and weather. Confederate infantry under D. H. Hill had taken position in it, and it made a natural trench. Wave after wave of Union troops came against it. The Irish Brigade, among others, attacked with great courage and lost heavily.

For hours the lane held. Then a mistake on the Confederate side, a misunderstood order that caused a regiment to leave its place, gave the Union troops an opening. They climbed to the edge of the road and fired down the length of the lane, and the Confederates in it were shot down in rows. The lane became known as Bloody Lane, and it earned the name. A Union breakthrough here, in the center, might have won the battle. It did not happen. The attackers were exhausted, and the Union commander, McClellan, held back reserves of thousands of men who had not been committed. The Confederate center was bent, but it did not break.

Afternoon: Burnside's Bridge

On the southern end of the field, a stone bridge crossed Antietam Creek. Ambrose Burnside, commanding the Union left, had been ordered to cross and attack. Confederate sharpshooters on the heights above the bridge, a force of about five hundred men, mostly from Georgia, held off the Union assaults for hours. In the early afternoon, after repeated attacks, they took it. Then there was a long delay for reorganization, and when Burnside's corps finally advanced toward Sharpsburg in the afternoon, it nearly cut off Lee's line of retreat.

At that moment, A. P. Hill's division arrived on the field. They had marched some fifteen to seventeen miles from Harpers Ferry, where Jackson had left them to take the surrender. They struck Burnside's flank, and the Union advance collapsed. It is one of the great timely arrivals of the war, and it saved Lee's army. The fighting wound down at dusk.

The cost

Then came the count. The commonly cited figures for the battle are roughly twelve thousand four hundred Union casualties and about ten thousand three hundred Confederate casualties, a total of something like twenty-two thousand seven hundred killed, wounded and missing in a single day. Those numbers include the wounded and missing, and some of the wounded died in the following weeks. Historians differ by a few hundred on the exact tally, and I will give you the round number: some twenty-three thousand. No other single day of combat in American history has produced a comparable total.

Think about what that number means. It happened in a farming country where the people had come out to see an army and found a slaughterhouse. The photographs of the dead, taken by Alexander Gardner within days of the battle, were displayed in New York in October, and the public that saw them understood the war in a way that newspaper columns had not made plain. Brady's gallery in New York exhibited them as "The Dead of Antietam," and for many Americans it was a first look at the dead of their own war in pictures.

Clara Barton also brought wagons of supplies to the battlefield, and, according to the National Park Service, she provided surgeons with desperately needed medical supplies.

McClellan's caution

Through the day of September 18, Lee's army stood in place, expecting a renewed attack. McClellan had, by some accounts, many thousands of fresh troops in reserve. He did not attack on the 18th. That night Lee withdrew across the Potomac into Virginia.

Criticism of McClellan has hardened over the years, and I think it is mostly deserved, with one qualification. He believed himself outnumbered, partly because his intelligence consistently overestimated Lee's strength. He was careful of his army, and some of that care was commendable. But a commander who has his enemy cornered against a river, and who lets him cross it, has missed a decision that could have ended the war in the east. Lincoln urged him to pursue, and McClellan again moved slowly. In early November Lincoln removed him from command. The two men had a quarrel that went beyond tactics: McClellan was a Democrat who wanted a limited war to restore the Union, and a Lincoln who was moving toward a harder war could not work with him.

The announcement

Now the consequence that matters most. Lincoln had been considering emancipation for months. He had told his cabinet in July 1862 that he intended to issue a proclamation, and Secretary of State William Seward had advised him to wait for a military victory, so the document would not look like a desperate gesture from a government in retreat. Lincoln agreed. Antietam gave him the victory, imperfect as it was.

On September 22, 1862, five days after the battle, Lincoln issued the Preliminary Emancipation Proclamation. Washington, which usually needs a committee to rename a post office, got a decision of this size from one man and a pen. Its central language was this: on the first day of January, 1863, "all persons held as slaves within any State, or designated part of a State, the people whereof shall then be in rebellion against the United States shall be then, thenceforward, and forever free." The final proclamation, issued on January 1, 1863, applied to the states and parts of states still in rebellion.

I want you to see the constitutional shape of this, because it matters. Lincoln did not claim that the President had a general power to abolish slavery. He rested the proclamation on his authority as Commander in Chief under Article II, as a war measure against states in rebellion. It did not apply to the border states that had stayed in the Union, and it did not touch slavery in them. Critics at the time and since have noted these limits. The proclamation could be defended in law as a war measure, but it was not itself a permanent abolition, and Lincoln knew it. That is why he pressed for the Thirteenth Amendment, which did what no proclamation could, and which was ratified in December 1865. The amendment's second section and what it gave Congress is the subject of The 13th Amendment's Second Section Gave Congress a New Kind of Power.

The foreign dimension

The announcement also changed the diplomacy. Britain and France had been considering mediation, even recognition. Lee's invasion, had it succeeded, might have tipped them. After Antietam and the proclamation, any government that recognized the Confederacy would be seen as taking the side of slavery in a war that had become, formally, a war against it. The British public, in particular, was strongly antislavery. The cause of the Confederacy abroad never recovered.

The objection and the answer

A thoughtful critic raises this objection. The Emancipation Proclamation was a calculated military and political move, not the expression of a moral awakening. It freed slaves only where Lincoln had no power to enforce it and left slavery in place where he did. Treating Antietam as a turning point toward liberty is therefore sentimental. The war began as a war for the Union, as the question of What Caused the Civil War, Who Won It and Why, Answered From the Record takes up at length, and Lincoln's own letter to Horace Greeley in August 1862 said that his paramount object was to save the Union, and not either to save or to destroy slavery.

That objection has something to it, and Lincoln himself would have agreed that the proclamation was a war measure. But the answer is in four points.

One. A war measure can also be a moral act. Lincoln hated slavery and said so for decades. He believed he lacked the constitutional power to end it where it existed in peacetime, and so he used the power he did have. That is the conduct of a man restrained by the Constitution, not of a man who does not care.

Two. The proclamation changed the war. It made emancipation a Union war aim and opened the Army to Black soldiers, who would serve in the tens of thousands, as the story of The 54th Massachusetts at Fort Wagner and the Soldiers Who Proved Doubters Wrong shows. Every Union victory thereafter was a victory for freedom.

Three. The legal restraint was a virtue. A President who does not claim power the Constitution does not give him is a President who can be trusted. The Thirteenth Amendment came through the proper process.

Four. The timing was prudence. Seward was right: a proclamation after a defeat would have looked like desperation. Lincoln waited for strength. That is statesmanship, and not cynicism.

What Antietam means

Antietam was a drawn battle in tactical terms and a decisive one in strategic terms. Lee's invasion failed. The Union held its ground and its nerve. And the war, from September 1862, was fought for a larger purpose. The cost was twenty-three thousand casualties in a day. The result was a country that, within three years, would end slavery by constitutional amendment.

The speech Lincoln gave at the cemetery the next year, read closely in The Gettysburg Address Read Closely Sentence by Sentence, put into words the purpose that Antietam had made official. That is worth remembering when we hear that history is only a catalog of failures. It is also a record of what free people are willing to pay for the thing they believe in, and of how a self-governing nation, even in a war it was nearly losing, kept to its Constitution and widened its freedom.

The case in brief

1. Lee invaded Maryland in September 1862, split his army to take Harpers Ferry, and lost the secret of his plan when Special Order 191 was found on September 13.
2. On September 17, the fighting at the Cornfield, the Sunken Road and Burnside's Bridge produced roughly 23,000 casualties, the bloodiest single day in American history.
3. McClellan, with a decisive advantage and his enemy against a river, held back and let Lee cross the Potomac.
4. Lincoln, waiting on Seward's advice for a victory, announced the Preliminary Emancipation Proclamation on September 22, 1862, resting it on his war powers as Commander in Chief.
5. The proclamation changed the war's aim and its diplomacy, and the permanent end of slavery came through the Thirteenth Amendment.

What you can do: read the Preliminary Emancipation Proclamation of September 22, 1862 and the Thirteenth Amendment side by side on the National Archives site, and note exactly what each one does and does not do.