Civil War Series Analyzes America’s Deadliest One-Day Battle

casualties at antietam totaled 23,000

By Jonny Lupsha, Wondrium Staff Writer

The Battle of Antietam was a key point in American Civil War history. It happened in Maryland and involved bold moves by both the Confederacy and the Union. What made the Battle of Antietam so deadly?

"Battle of Antietam" by Kurz & Allison
The Battle of Antietam, fought on September 17, 1862, was the deadliest single-day battle in American history. Illustration by Kurz and Allison / Wikimedia Commons / Public Domain

Emboldened by a Confederate victory at Second Manassas, Gen. Robert E. Lee took the fight to the Union near Sharpsburg, Maryland, in what would become the Battle of Antietam. The battle occurred in multiple phases throughout the day and resulted in a death toll of over 3,600—and a total of 23,000 casualties when adding in the missing, captured, and wounded. This makes it the deadliest single-day battle in American history.

Why was Antietam so deadly? In their video series The Great Tours: Civil War Battlefields, Dr. Peter Carmichael, the Robert C. Fluhrer Professor of Civil War Studies at Gettysburg College, and Dr. Caroline Janney, the John L. Nau III Professor in History of the American Civil War at the University of Virginia, explore Antietam’s bloody legacy.

Why Did the Confederacy Move into Maryland?

“Lee wasted very little time after Second Manassas in preparing to go into Maryland, and his decision was shaped by several factors,” Dr. Janney said. “First, he put his faith in the offensive as the best chance to achieve a victory of annihilation over Union armies. He also sought logistical relief for the Confederate home front, given that northern and central Virginia had been occupied by armies with voracious appetites for food and fodder.”

And what kind of “logistical relief” did Lee hope for in Virginia? Both armies had picked the resources in their areas clean, from tearing down fences for campfires to drinking local wells dry. This was because resources were already strained with one army stationed in an area, so when a battle brought both sides to one location, supplies became unsustainable.

Lee also hoped that by bringing his force into new territory further north, he could refill his ranks with new recruits.

“Maryland had many Southern sympathizers, mostly in eastern Maryland, but Lee’s army was headed into Unionist-dominated western Maryland,” Dr. Janney said. “His soldiers were bitterly disappointed when Marylanders did not greet them as liberators.”

Why Was the Battle of Antietam So Deadly?

The Battle of Antietam was fought on September 17, 1862. Union forces were led by Maj. Gen. George McClellan. According to Dr. Carmichael, one incident at the beginning of the fight helped cause the high number of casualties. Three Union brigades attacked the Confederate brigades stationed at the left flank near a cornfield at Antietam. Only one Union brigade made it through initially, led by Lt. Col. Jacob Eugene Duryée.

“[Duryée’s men] ran smack into a Confederate line,” Dr. Carmichael said. “That initiated a series of attacks back and forth—the fighting is extraordinarily fluid. What people need to imagine, again, is that one side has an upper hand, and just when they’re about to deliver that knockout blow, reinforcements arrive on the other side and it goes back and forth and back and forth.”

This very brief tug of war between the Union and the Confederacy alone, nonetheless, caused a full one-third of the battle’s casualties. Shortly afterward, a different group of 5,000 Union soldiers, led by Maj. Gen. John Sedgwick, marched to attack the same Confederate left flank. Having missed the initial fight, they believed there were very few Confederates there and, thus, chose to march in very tight brigade-length battle lines, making it difficult to maneuver. They were surprised by Lee’s men, essentially surrounded, and suffered heavy losses.

“You should note that [Maj. Gen. Edwin] Sumner was so rattled by what happened in the West Woods that he reported to McClellan basically that nothing more could be done on that flank,” Dr. Carmichael said. “Here’s again another example of the back and forth, savage, fierce fighting. It almost always ends in a draw; and that’s what happens.”

Repeated stalemates throughout the day led to a spike in casualties for both sides.

The Great Tours: Civil War Battlefields is now available to stream on Wondrium.

Edited by Angela Shoemaker, Wondrium Daily