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The Battle of Antietam

Written by: Mackubin Owens, Foreign Policy Research Institute

By the end of this section, you will:

  • Explain the various factors that contributed to the Union victory in the Civil War

Suggested Sequencing

Use this Narrative with the Mathew Brady, The Dead of Antietam Photography, 1862 Primary Source to allow students to see and analyze images from this battle.

September 17, 1862 was the bloodiest day in American history. On a very small patch of land near Sharpsburg, Maryland, nearly 22,000 Americans shed their blood and 6,000 of them died. Anyone who has visited Antietam cannot help but be struck by the compactness of the battlefield in which so many men lay.

The lithograph shows Union and Confederate forces meeting at the Battle of Antietam. Union forces cross a bridge to meet the Confederates. Several men on both sides lie on the ground. Smoke from guns and cannons dots the scene.

This 1888 depiction of the Battle of Antietam shows Union forces on the left and Confederate forces on the right.

But the battle’s importance transcends the number of casualties. On the one hand, it represented the apex of the Confederacy’s offensive military action at that point in the war. On the other, it provided President Abraham Lincoln an opportunity to alter the character of the war by officially launching an attack on the institution of slavery, which the great abolitionist Frederick Douglass called “the stomach of the rebellion.”

To fully understand the importance of the battle of Antietam (also called Sharpsburg), it is necessary to place it in its broader political and military context. The federal government had no constitutional authority over slavery in the states where it already existed. But secession by the slave states opened a constitutional way for Lincoln to end slavery immediately with uncompensated emancipation, because of his war powers as commander-in-chief.

Some Union commanders had treated slaves as contraband of war, meaning captured enemy property – in this case, humans. Others, such as John C. Fremont and David Hunter, had resorted to martial law to free slaves, which Lincoln reversed because they had no authority to do so, and he feared it would cause the border states such as Maryland, Kentucky, and Missouri to secede. In 1861 and 1862, Congress passed two confiscation acts, which allowed some confiscation of Confederate property, including slaves. For Lincoln, all these approaches were of questionable constitutionality. Only a proclamation based on the president’s war power in response to a rebellion would meet constitutional muster.

But Lincoln had to proceed with prudence to maintain a working coalition between members of his Republican Party, who favored emancipation, and War Democrats in the North, who were willing to fight to restore the Union but did not wish to interfere with slavery. In addition, to issue an emancipation proclamation while Lee was defeating Union armies in Virginia would seem to smack of desperation. Lincoln needed a military victory.

In early 1862, General Ulysses S. Grant won a costly victory at Shiloh and captured the critical railroad junction at Corinth, Mississippi. In addition, New Orleans fell to Union forces, which now controlled most of the Mississippi River. However, General George McClellan failed in his bid to take Richmond in the Peninsular Campaign during the Seven Days’ Battle. By the end of August, Lee had shattered Pope’s army at Second Bull Run, or Second Manassas, but had not quite annihilated it. Lee now saw an opportunity to deliver a knockout punch to the Union by invading Maryland to lure McClellan into a battle in which Lee would accomplish what he had almost realized at Second Manassas: the destruction of a major Union army, this time on Union soil.

By invading Maryland, Lee sought nothing less than to change the character of the war. Consistent with his operational approach, he intended to execute a strategic turning movement and destroy McClellan’s army, thereby convincing the population of the North to give up the fight to subdue the South and winning European support for the Confederacy.

The time appeared “propitious,” as Lee wrote to Jefferson Davis, the president of the Confederacy, to invade Maryland. Not only had Lee’s efforts during the Seven Days’ Battle and at Second Bull Run been crowned with success, he also knew that with the April Conscription Act, the Confederacy had exerted its maximum effort to bring troops into the field, whereas the North had barely tapped its potential to raise armies.

But Lee’s plan began to go awry ten days after he crossed the Potomac into Maryland on September 4. The main problem was his decision to capture Harpers Ferry, believing the garrison there presented a threat to his lines of communication. To do so, Lee had to divide his force. This in itself had never been a problem for him, but now he had to act in ignorance of McClellan’s location.

Lee dispatched “Stonewall” Jackson to capture Harpers Ferry, assuming the garrison would either flee or surrender quickly. Meanwhile, he sent his other corps under General James Longstreet to Boonsboro to guard against what he expected to be a characteristically cautious approach by McClellan. But the garrison at Harpers Ferry did not behave as Lee expected, and the local topography forced Jackson to divide his corps into three columns. This disrupted Lee’s timetable and put his divided force at risk, because McClellan’s advance toward western Maryland was much more rapid than Lee expected. However, McClellan, still overly cautious, failed to take advantage of Lee’s divided forces, even after two Union soldiers discovered Lee’s plans on the ground wrapped in three cigars.

Lee struggled to reunite his army before McClellan arrived. Longstreet attempted to delay the Union advance at South Mountain, but, on September 14, the advance guard of the Army of the Potomac dislodged the Confederates from their defensive position at Turner’s Gap. Harpers Ferry finally capitulated on September 15, and except for A.P. Hill’s division, which remained to parole the 12,500-man garrison, Jackson hurried to rejoin Lee, who had taken up a position near Sharpsburg, Maryland.

Even with a reunited army, however, Lee’s ability to stand and fight was severely limited. His soldiers had been scattered across western Maryland from Hagerstown to Pleasant Valley by the heat, the forced marches, and the confusion of retreats. Lee had asked too much of them. As a result, when McClellan unleashed his attack at dawn on September 17, Lee’s army (38,000 troops) was only half the strength of McClellan’s (76,000 troops).

The first action of the day took place on the Union right, as first Joseph Hooker’s corps and then Joseph Mansfield’s hammered the Confederate left. The battle raged back and forth at the West Woods, the Dunker Church, and David Miller’s cornfield. The Union troops surged forward, only to be driven back by desperate Confederate counterattacks. When asked where his division was, John Bell Hood replied, “Dead on the field.”

As the fighting on the Union right ebbed, it surged across the center. After repeated failed assaults against the main Confederate defensive position, which ran along a sunken road, one Union division was able to flank it, delivering deadly fire. As the dead filled the sunken road, which came to be known as “Bloody Lane”, the Confederate center collapsed. Lee was able to patch together a defense, but had McClellan committed his reserve at this point, Lee’s army might well have been annihilated.

Figure (a) shows many men lying in a ditch, dead. Two men stand on the edge and look. The land behind them is bare. Figure (b) shows a sunken dirt road running between two wooden fences. There is an informational sign in the foreground. There is a statue of a soldier in the background.

Compare (a) a photograph of a section of “Bloody Lane” after the Battle of Antietam with (b) a photograph of “Bloody Lane” today.

Meanwhile, the action shifted to the Union left, where Ambrose Burnside’s corps was stymied by a small detachment of rebels in its attempt to cross a bridge over Antietam Creek (the stream was fordable further to the south). Finally, in the middle of the afternoon, Burnside carried the bridge and was pressing the Confederates back toward Sharpsburg. On the cusp of victory, however, his unit was struck on the flank by A.P. Hill’s division returning from Harpers Ferry. Lee was able to hold his position, but barely.

Lee remained at Sharpsburg the next day, but McClellan refused to renew the battle. Although his casualties were heavy (12,400 dead, wounded, and missing), Lee’s were proportionately heavier (10,300 among his smaller force). In addition, McClellan had a fresh reserve corps that was never committed. Under cover of darkness, Lee slipped away. When McClellan belatedly followed on September 19, his vanguard was repulsed at Shepherdstown. Lincoln was irate that McClellan had let Lee get away, but the president had the victory he needed for his Emancipation Proclamation as southern troops retreated from the North and were prevented from taking Washington, DC.

The photograph shows Lincoln and McClellan sitting in a tent. There is an American flag draped on the table behind Lincoln.

This 1862 photograph shows President Lincoln, left, and General McClellan meeting after the Battle of Antietam.

Lee’s ascent was one factor that changed the character of the war. Had he not emerged at this time, the Civil War might well have ended in 1862, with the seceded states returning to the Union and slavery intact. Instead, under Lee’s aggressive military direction, the conflict became an all-out war that concluded only with the complete subjugation of the South and the end of slavery.

The second factor that changed the character of the war was the opportunity the battle provided Lincoln to issue the Emancipation Proclamation. Lincoln issued the preliminary Emancipation Proclamation on September 22, giving the Confederate states until January 1, 1863, to give up the rebellion and keep their slaves. If they did not, the Emancipation Proclamation would go into effect and the slaves would be freed. The document did not free the slaves in the border states, because Lincoln had no constitutional authority to do so in states that were not at war with the United States. With the Emancipation Proclamation, however, the war to save the Union also became a war for human liberty and equality.

Review Questions

1. Which Union general led the army to victory over the Confederate army at Antietam?

  1. Ulysses S. Grant
  2. William T. Sherman
  3. Robert E. Lee
  4. George B. McClellan

2. What did Abraham Lincoln claim granted him the constitutional power to issue the preliminary Emancipation Proclamation in September 1862?

  1. The president’s legislative power
  2. The president’s war power as commander-in-chief
  3. The president’s judicial power
  4. The president’s authority as chief executive

3. Why did President Lincoln reverse the use of martial law by some of his generals when they liberated freed slaves?

  1. Lincoln feared the border states might secede from the Union.
  2. The treatment of the freed slaves was inhumane.
  3. The freed slaves could not be cared for by the Union army.
  4. Lincoln feared the freed slaves might start their own rebellion.

4. What was the main goal of the War Democrats from the North?

  1. To end the war immediately, allowing the Confederacy to remain outside the union
  2. To emancipate the slaves
  3. To restore the Union
  4. To undermine the efforts of President Lincoln’s war policy

5. After the Battle of Antietam prevented a successful invasion of the Union, President Lincoln understood

  1. the aim of the war must be changed to completely defeating the South
  2. the focus of the war needed to change to keep the number of casualties down
  3. General McClellan needed to change his strategy and become more aggressive in his battle tactics
  4. Virginia must be captured to force a Confederate surrender

6. Immediately preceding the Battle at Antietam, Confederate General Robert E. Lee’s confidence was boosted by a victory at

  1. Sharpsburg
  2. Harpers Ferry
  3. Manassas
  4. Turner’s Gap

7. Compared with the Confederacy, Union forces at Antietam

  1. suffered higher casualties
  2. were routed by Lee’s cavalry
  3. aggressively pursued the enemy after the battle
  4. had no reserve corps

Free Response Questions

  1. Describe General Robert E. Lee’s motivation for invading Union territory in September 1862.
  2. Explain why Abraham Lincoln waited until after the Battle of Antietam to issue a preliminary version of the Emancipation Proclamation.

AP Practice Questions

“Be it enacted by the Senate and House of Representatives of the United States of America in Congress assembled, That if, during the present or any future insurrection against the Government of the United States, after the President of the United States shall have declared, by proclamation, that the laws of the United States are opposed, and the execution thereof obstructed, by combinations too powerful to be suppressed by the ordinary course of judicial proceedings, or by the power vested in the marshals by law, any person or persons, his, her, or their agent, attorney, or employé, shall purchase or acquire, sell or give, any property of whatsoever kind or description, with intent to use or employ the same, or suffer the same to be used or employed, in aiding, abetting, or promoting such insurrection or resistance to the laws, or any person or persons engaged therein; or if any person or persons, being the owner or owners of any such property, shall knowingly use or employ, or consent to the use or employment of the same as aforesaid, all such property is hereby declared to be lawful subject of prize and capture wherever found; and it shall be the duty of the President of the United States to cause the same to be seized, confiscated, and condemned.”

First Confiscation Act, approved August 6, 1861

Refer to the excerpt provided.

1. Persons living in the Confederacy would object to the law from which the provided text was excerpted because in their opinion it violated

  1. states’ rights
  2. property rights
  3. international law
  4. limits on presidential power

2. The main motivation for Congress to pass the law containing the provided excerpt was to

  1. penalize those in rebellion against the U.S. government
  2. gain wealth to purchase war supplies
  3. ensure Great Britain’s neutrality in the war
  4. disrupt Confederate supply lines

Primary Sources

Lincoln, Abraham. “The Emancipation Proclamation.” January 1, 1863.

Suggested Resources

Guelzo, Allen. Lincoln’s Emancipation Proclamation: The End of Slavery in America. New York: Simon and Schuster, 2004.

Harsh, Joseph L. Confederate Tide Rising: Robert E. Lee and the Making of Southern Strategy, 1861-1862. Kent, OH: Kent State University Press, 1998.

Harsh, Joseph. Taken at the Flood: Robert E. Lee and Confederate Strategy in the Maryland Campaign of 1862. Kent, OH: Kent State University Press, 2000.

McPherson, James M. Battle Cry of Freedom: The Civil War Era. Oxford, UK: Oxford University Press, 1988.

McPherson, James M. Crossroads of Freedom: Antietam, The Battle that Changed the Course of the War. Oxford, UK: Oxford University Press, 2002.

Oakes, James. Freedom National: The Destruction of Slavery in the United States, 1861-1865. New York: W. W. Norton, 2014.

Owens, Mackubin T. “From Beaver Dam Creek to Antietam: Lee’s Virginia-Maryland Campaign of 1862.” 2007.

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