Who Won the Battle of Antietam?

In September 1862, as the American Civil War dragged on, the South gambled on taking the war into the North to pressure the Union and impress foreign powers.

Jan 8, 2024By Owen Rust, MA Economics in progress w/ MPA

who won battle of antietam


The South had a problem in 1862. Despite skilled battlefield leadership, the Confederacy had far less soldiers and industrial output than the United States. In a war of attrition, the South would eventually be ground under by the North’s massive industry and larger, immigration-boosted population. But could a surprise attack into the North itself be a game-changer to bluff the Union into abandoning its war to prevent Confederate secession?


Victory Goes to the Union…Sort Of

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An image of Union forces carrying the United States flag during the Battle of Antietam, via The Heritage Post


The American Civil War was fought as a largely defensive war by the Confederacy. A popular misconception, perhaps due to the historical fiction genre, is that the South could have won an outright military victory in the conflict. Lacking the manpower and industrial output of the North, the South simply hoped to hold off invasion long enough for the United States to allow the Confederacy to continue to exist. However, the first year of the war revealed more political willpower from the North than was expected; the United States was willing to fight to preserve the Union!


On September 17, 1862, the Union won a relative military victory in Washington County, Maryland, near the small town of Sharpsburg. The Confederacy, under General Robert E. Lee, had invaded the Union state of Maryland, adjacent to the Confederate capital of Richmond, Virginia, in hopes of sparking a panic. Instead, Lee was forced to withdraw back to Virginia. However, attempts to pursue Lee’s retreating army were defeated. The South could arguably claim victory in that it invaded the North and inflicted more casualties on the Union army than it received in return, but the North could also claim victory in that it repelled the invasion and inflicted almost as many casualties on an opponent that could scarcely afford them.


Timeline of the Battle of Antietam

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A map and time of important American Civil War battles during the second year of the conflict (April 1862 – April 1863), including the Battle of Antietam, via the Library of Congress


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On September 3, 1862, the Confederacy began to launch an unprecedented attack into Union territory, urged by Confederate President Jefferson Davis. Before that time, the South had fought an entirely defensive war.


By September 6, Confederate generals Robert E. Lee and Thomas J. “Stonewall” Jackson had crossed the Potomac River into Maryland, engaging in a de facto invasion of the North. Lee proclaimed that his occupation of Maryland was not hostile and would give citizens of the border state a chance to decide their own fate, referencing the Union’s suspension of habeas corpus (right to appeal) for arrested Marylanders.


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A map showing movements of Union and Confederate armies during the Battle of Antietam in September 1862, via the National Park Service


During this time, beginning on September 5, the Union army led by General George McClellan began moving to meet the invaders.


On September 13, the Confederates occupied a number of Maryland towns, but on September 14, the Union army arrived in force.


The next day, Robert E. Lee consolidated his forces at Sharpsburg, where he was joined by “Stonewall” Jackson on September 16.


The Battle of Antietam began at dawn on September 17 and lasted for approximately 12 hours. When it grew dark that evening, Lee began to withdraw across the Potomac River, returning to Virginia.


By mid-day on September 19, Confederate forces were all back in Virginia (Confederate territory).


What Caused the Battle of Antietam?

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A photograph of Union general Ulysses S. Grant, whose April 1862 victory in the Battle of Shiloh led to the Confederacy’s gamble of invading the North, via the National Geographic Society


The South’s unsuccessful invasion of the North in September 1862 was prompted by a Union victory in the Battle of Shiloh five months earlier. Shiloh had been the bloodiest battle in the war to date and saw a larger Union army led by new commander Ulysses S. Grant defeat a smaller Confederate force led by Albert Sidney Johnston. After Johnston died in battle on April 6, he was replaced by General Pierre G.T. Beauregard, who eventually retreated on April 7 when he realized that he was heavily outnumbered by Union troops. Grant’s willingness to fight aggressively and suffer high casualties signaled that the North could not be simply held off forever.


The South wagered that it could frighten the United States into an armistice by invading the North and causing panic. Simultaneously, both Confederate General Robert E. Lee and President Jefferson Davis believed that a decisive military victory during an invasion of the North would finally win over British and French political (and hopefully military) support for the Confederacy.


At the outset of the American Civil War, both European powers imported lots of cotton from the American South, and the Confederacy hoped that cotton diplomacy – and a chance to weaken the United States as a potential rival power – would lead to diplomatic recognition by France and Britain. During the war, France took advantage of Americans’ preoccupation to seize Mexico as a colony, sparking a second Mexican War of Independence.


Why Was the Battle of Antietam Significant?

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A painting of the infamous Battle of Antietam, which remains the bloodiest single day in US history, via the Antietam Institute


The Battle of Antietam replaced the Battle of Shiloh as the single bloodiest day in US history, with both sides accumulating some 23,000 casualties on September 17, 1862. Aside from its intensity, the battle was also significant due to the change in Confederate strategy: it would fight aggressively to sap the North’s morale and political will. The Confederacy was also taking significant risks, given its relative lack of manpower and industrial output compared to the Union, to win foreign recognition. A decisive Confederate victory at Antietam may have convinced Britain and France that the South could win the war and was a worthy investment of military aid.


However, the Confederacy lost the battle, marking it as one of the turning points in the war. The repulsion of the invasion increased morale in the North, making it less likely that the South could simply wear down the Union’s political will. The victory gave a political opening to US President Abraham Lincoln, who had been waiting for such a victory to issue his now-famous Emancipation Proclamation. With a Union victory at Antietam signaling strength, Lincoln was able to declare that all enslaved people in Confederate territory would be free as of January 1, 1863. This marked a more aggressive stance by the Union, which had thus far not addressed slavery as part of the war.


5 Facts About the Battle of Antietam

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A photograph from Alexander Gardner, whose photographs from the Battle of Antietam shattered public misconception of war as glorious, via The Metropolitan Museum of Art, New York


1. Casualties

Although victorious, the Union suffered over 2,100 soldiers killed compared to the Confederacy’s 1,500. When including the 9,500 wounded Union soldiers and 7,800 wounded Confederates, plus about 1,000 missing or captured on both sides, this amounted to almost 23,000 casualties. Despite having suffered more casualties, Union General George McClellan was criticized after the Battle of Antietam for not being more aggressive and pursuing a retreating Robert E. Lee.


2. Commanders

The Union army was led by George B. McClellan, a Pennsylvanian from an upper-class family. Like many of his cohorts, McClellan was a West Point graduate and a veteran of the Mexican-American War. From working in Illinois during the 1850s on the railroad, he came to know a local politician named Abraham Lincoln. Despite having known Lincoln before the war, McClellan faced criticism after the Battle of Antietam for being excessively slow and cautious, resulting in his replacement by General Ambrose Burnside that autumn.


Generals Robert E. Lee and Thomas J. “Stonewall” Jackson were the two Confederate commanders in the battle, with Lee as commander-in-chief of the Army of Northern Virginia. This was the Confederacy’s most powerful army, which stood between the Confederate capital city of Richmond, Virginia and the US capital of Washington DC. Both Lee and Jackson were, like McClellan, West Point graduates who had served in the Mexican-American War. Unlike McClellan, both Southerners were renowned for their tactical skill and aggression in warfare. While McClellan and Lee survived the war, “Stonewall” Jackson died of pneumonia one week after the Battle of Chancellorsville in May 1863.


3. Number of Forces Involved

McClellan commanded some 87,000 Union troops, far outnumbering Lee’s 45,000 Confederate soldiers. Given McClellan’s overwhelming advantage in manpower, his refusal to pursue Lee during the Confederate retreat across the Potomac after September 17 upset US President Abraham Lincoln. However, Lee was able to defeat an army almost twice his size, which he did the following spring in the Battle of Chancellorsville, where 57,000 Confederates won a surprise victory over almost 100,000 Union troops.


4. Visiting Antietam

Antietam National Battlefield has been well-equipped to handle tourists since 1963. The visitor center is open from 9:00 AM to 5:00 PM on most days. There is also a museum with a gift shop, the ability to listen to battlefield tours narrated by park rangers and take a self-guided automobile tour on an eight-and-a-half mile road with eleven stops. Visitors who want to spend ample time at the battlefield can stay in nearby historic Sharpsburg, Maryland.


5. Trivia: Famous Photography Shatters War Myths

With technology finally making cameras (relatively) transportable, the American Civil War became the first military conflict to be significantly photographed. This largely began, however, with the Battle of Antietam. Photographer Alexander Gardner became one of the first to take photos of the dead on the battlefield. His work immediately after the Battle of Antietam was credited with bringing Americans the sobering reality of war for the first time. In the future, fewer would mindlessly accept political leaders pushing the nation into armed conflict.


The Aftermath of the Battle of Antietam

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An image of the Emancipation Proclamation text superimposed over freed enslaved people (left) and Union President Abraham Lincoln and his administration (right), via the Sutherland Institute


Militarily, the battle was largely a draw, with both sides able to argue that a victory had been won. Politically, however, the Union won a tremendous victory. The Confederacy never did receive support from Britain and France. The Emancipation Proclamation, issued on September 22 by Abraham Lincoln, galvanized European public support against the slave-owning Confederacy. Both Britain and France had already abolished slavery, making it politically risky to publicly support the South. Additionally, both powers also traded with the North and did not want to lose trade with the industrialized Union by formally supporting the agricultural Confederacy.


The Civil War became more aggressive after Antietam, likely due to the Confederacy realizing that lack of foreign support meant it was on borrowed time. In 1863, Robert E. Lee would again decide to invade the North after a series of victories. For the Union, the Emancipation Proclamation gave a moral cause for fighting aggressively to win the war. Instead of simply trying to prevent Southern states from seceding, the Union was now fighting to abolish a moral and ethical wrong. This would make it more difficult for the South to wear down the North’s willpower and secure any sort of armistice.

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By Owen RustMA Economics in progress w/ MPAOwen is a high school teacher and college adjunct in West Texas. He has an MPA degree from the University of Wyoming and is close to completing a Master’s in Finance and Economics from West Texas A&M. He has taught World History, U.S. History, and freshman and sophomore English at the high school level, and Economics, Government, and Sociology at the college level as a dual-credit instructor and adjunct. His interests include Government and Politics, Economics, and Sociology.