Antietam (1862): The Real Bloodiest Single Day in American History

Military History: The US Civil War

Chapter 5 · Antietam (1862): The Real Bloodiest Single Day in American History

By September 1862 the Confederacy had seized the initiative in the East, and Robert E. Lee carried the war into the North for the first time. Near the small Maryland town of Sharpsburg, his army and McClellan's met in a battle that produced more casualties in one day than any other in American history. It was a tactical draw — and one of the war's most important political turning points.

How Lee Got to Maryland

  • Spring 1862 McClellan, who rebuilt the army after Bull Run (Chapter 3), lands it on the Virginia Peninsula and advances slowly on Richmond.
  • June 1862 The Confederate commander Joseph Johnston is wounded; Robert E. Lee takes command of what he names the Army of Northern Virginia.
  • June–July 1862 In the Seven Days Battles, Lee attacks repeatedly and drives McClellan back from Richmond, despite heavy Confederate losses.
  • August 1862 Lee defeats a separate Union army at Second Bull Run.
  • September 1862 Lee crosses the Potomac into Maryland.

Why Invade?

To move the fighting out of war-damaged Virginia, feed his army from Northern farms, encourage pro-Southern feeling in Maryland, and win a victory on Union soil.

The Bigger Prize

A major victory in the North might push Britain and France toward recognising the Confederacy, and strengthen Northern politicians who wanted a negotiated peace before the November elections.

The Lost Order

Special Order 191, found 13 September 1862

Lee boldly split his army into several parts; Stonewall Jackson was sent to capture the Union garrison at Harpers Ferry. At a campsite near Frederick, Maryland, two soldiers of the 27th Indiana found a copy of Lee's orders setting out the whole plan, wrapped around three cigars. It reached McClellan the same day.

The Greatest Intelligence Coup of the War — Used Slowly McClellan knew exactly where Lee's scattered army was. He reportedly said, "Here is a paper with which if I cannot whip Bobbie Lee, I will be willing to go home." But he waited about 18 hours before moving, and then advanced cautiously. That gave Lee time to start pulling his army back together.

On 15 September Jackson captured Harpers Ferry and more than 12,000 Union soldiers — the largest surrender of US troops until the Second World War — then hurried to rejoin Lee at Sharpsburg.

The Battle: 17 September 1862

Union (McClellan)Confederate (Lee)
EngagedAbout 72,000About 38,000
KilledAbout 2,100About 1,550
Total casualties (killed, wounded, missing)About 12,400About 10,300

McClellan attacked in three separate phases, one after another, rather than all at once. That let Lee move his outnumbered troops from one threatened point to the next.

Morning · The Cornfield

Union attacks on the Confederate left, around a farmer's cornfield and a small Dunker church, met Jackson's troops. The field changed hands again and again — by one count at least 15 times — with appalling losses on both sides.

Midday · The Sunken Road ("Bloody Lane")

In the centre, Confederates held a farm road worn down below ground level, forming a natural trench. After hours of assaults, Union troops got a position where they could fire straight down the road; the defenders were cut down and the line broke. The Confederate centre was open — but McClellan kept thousands of fresh reserve troops out of the fight rather than send them through the gap.

Afternoon · Burnside's Bridge

On the Union left, General Ambrose Burnside spent hours trying to force his way across a narrow stone bridge over Antietam Creek, held by a few hundred Georgia riflemen. When his troops finally crossed and began pushing toward Sharpsburg, A.P. Hill's division arrived around 3:30 p.m. after a hard march from Harpers Ferry and struck their flank. The Union advance was driven back.

Lee's Army Was Nearly Destroyed Lee fought with his back to the Potomac River and almost no reserves. Coordinated Union attacks, or the use of McClellan's unused reserves at Bloody Lane, could very likely have broken his army. Instead, Lee held his line, stayed on the field the next day, and withdrew across the Potomac on the night of 18–19 September. McClellan did not seriously pursue.
"Bloodiest Single Day" — What It Means About 22,700 men were killed, wounded, or missing in roughly twelve hours of fighting. That's the highest number of casualties from a single day of battle in American history, including later wars. Around 3,650 of those were killed outright; many of the wounded died in the days and weeks afterward.

Why a Draw Became a Turning Point

The Emancipation Proclamation

Lincoln had drafted a proclamation freeing enslaved people in rebel territory, but waited for a victory so it wouldn't look like desperation. Antietam was enough. He issued the preliminary proclamation on 22 September 1862, taking effect on 1 January 1863.

Europe Steps Back

Britain had been seriously considering offering to mediate between the two sides. Lee's retreat, and a war now openly about slavery, made intervention much less likely.

McClellan Goes

Frustrated by McClellan's slowness to pursue, Lincoln removed him from command on 5 November 1862 and replaced him with Burnside.

The Military Side of Emancipation The Proclamation was also a war measure. It encouraged enslaved people to flee to Union lines, weakening the Confederate economy and labour force, and it opened the way for Black men to enlist in the Union army — the roughly 180,000 soldiers mentioned in Chapter 1. The political and legal story belongs to US History; its military effects run through the rest of this course.
The First Battlefield Photographs of the Dead

Two days after the battle, photographers working for Mathew Brady, including Alexander Gardner, photographed bodies still lying on the field. When the images were shown in Brady's New York gallery in October 1862 as "The Dead of Antietam," they gave civilians a direct view of combat deaths for the first time.

Questions to Sit With

McClellan had Lee's plans and twice as many men. What seems to have stopped him from winning decisively?
Why might Lincoln have been right to wait for a victory before announcing emancipation?
How might photographs of the dead have changed how people at home thought about the war?

Quick Reference — Chapter 5

  • Lee took command in June 1862, drove McClellan from Richmond in the Seven Days, won at Second Bull Run, and invaded Maryland in September
  • Special Order 191 was found wrapped around cigars on 13 September; McClellan waited about 18 hours to act on it
  • Jackson captured Harpers Ferry and over 12,000 Union troops on 15 September
  • Antietam (Sharpsburg), 17 September 1862: about 72,000 Union vs 38,000 Confederate; three separate phases — the Cornfield, Bloody Lane, Burnside's Bridge; A.P. Hill arrived in time to save Lee
  • About 22,700 casualties, including about 3,650 killed — the bloodiest single day in American history
  • A tactical draw but a strategic Union success: Lee retreated, Lincoln issued the preliminary Emancipation Proclamation on 22 September, and European intervention became much less likely
  • McClellan was removed on 5 November 1862; Gardner's photographs showed the dead to the public

What's Next

Chapter 6: Gettysburg (1863): The Real Turning Point & Pickett's Charge.