Why Was the Battle of Antietam a Pivotal event in the American Civil War

President Lincoln with General McClellan at Antietam, October 1862

Gettysburg, perhaps the most renowned battle of the American Civil War, was the second incursion of Confederate troops onto Union soil. The first offensive in the North taken by General Robert E. Lee and his Army of Northern Virginia resulted in the Battle of Antietam. On September 17, 1862, Lee’s troops met Union forces, under the command of General George B. McClellan, in Sharpsburg, Maryland. In this one poignant moment in time, American history was forever altered. If Gettysburg was the most significant battle in terms of scope, Antietam (Sharpsburg to Southerners) was the most pivotal with respect to the aims of the war.

This battle changed the formally stated purpose of the war from one of states’ rights vs unification to one of the question of slavery. Although the “states’ rights” in question were the rights of each state to determine their positions on slavery, this was not officially recognized in the Confederate charter. In the North, a political game was afoot. Abolitionists, of course, fought adamantly to end the “peculiar institution,” while politicians cautioned of the ramifications of such a drastic step. One day in Maryland provided the catalyst needed to end the debate. The Battle of Antietam was the most pivotal event of the Civil War as it erased the threat of European recognition of the Confederate States of America (CSA) and was the impetus needed for the issuance of the Emancipation Proclamation.

What happened before Antietam

General George B. McClellan, from the Matthew Brady Studio.

May 1861 saw the establishment of a functioning Confederate government in Richmond, Virginia. CSA President Jefferson Davis and his armies were in control of nearly all of the 750,000 acres that were deemed CSA territory.[1] After the first shots of the war were fired a month prior in South Carolina, the Confederates became defenders. They simply needed to retain what they already possessed in order to prove victorious over the “invading” Yanks. Conversely, President Lincoln and the Union forces were tasked with subduing the Southern rebellion, controlling CSA lands, and reuniting the nation. This arduous endeavor seemed beyond the scope of McClellan and the Army of the Potomac in the eastern theater of the war.

General McClellan took charge of the massive army after the crushing Union defeat at the First Battle of Bull Run in July 1861. His overly cautious nature and misconceptions of his enemy’s strength caused him to resist attacking the Confederate armies, thereby making the Army of the Potomac unable to claim any victories in the East. At once, General Ulysses S. Grant had several great successes in the western theater of the war. His troops forced the unconditional surrender of Confederate garrisons at Forts Henry and Donaldson in February 1862 while by the conclusion of the following month, Union General Ambrose E. Burnside controlled all but one port in previously Confederate-held North Carolina.[2] Additional Union victories in Arkansas and Tennessee along with the capture of New Orleans and all of its ports gave citizens of the North great hope for a swift end to the war. Military strategists and politicians of the North; however, were not as optimistic as they were keenly aware that Union victory must come from the East; an opinion not lost on their European counterparts.

The CSA hoped to use Cotton to gain Foreign Recongnition

Mississippi cotton field and slave labor, date unknown

The summer of 1862 proved to be the most hopeful for the South with regard to British and French intervention on the behalf of the CSA. Although news took ten days to cross the Atlantic, European powers became increasingly aware of Lee’s victories in the eastern theater. News of Confederate success coincided with a massive shortage of cotton in Europe, particularly in England. Prior to the war, a full 80% of Britain and France’s raw cotton came from Confederate states. Until the summer of 1862, England was able to utilize the surplus of cotton they purchased from the exceptional crops of 1859 and 1861.[3] By May 1862, the supply was less than a third of what the mills required and the European textile industry was facing a crisis. Unemployment in Britain grew exponentially as 75% of cotton workers were unemployed or faced reduced work hours.[4] King Cotton still reigned supreme.

Confederate diplomats to France and England blamed the shortage on the Union Navy, claiming they were unable to maneuver their cargo ships through the blockade. This was a canard put forth in order to pressure England into breaking the blockade thus prompting a break in relations between the United States and Britain. In fact, the South enacted an embargo on cotton so as to add to the pressure faced by the British and French governments from their unemployed citizens. The strategy was beginning to work as the leading industry of England (textiles), was starting to shut down. Henry Adams, Secretary to the American Minister of London, wrote that “the suffering among the people in Lancashire and in France is already great and is increasing enormously.”[5] These working-class people were seeing the circumstances (understandably so) through a lens of familial and financial impact whereas others held more ideological views.

European nations disapproved of Slavery and were uncomfortable with CSA

Regardless of what rhetoric was used by the CSA government, there was a tacit understanding among the intellectuals and politicians of Europe that the war was, in large part, about the issue of slavery. English philosopher John Stuart Mill believed that a southern victory “would be a victory of the powers of evil which would give courage to the enemies of progress and damp the spirits of its friends all over the civilized world.”[6] Karl Marx, who had been exiled from Germany and was living in London at the time, claimed that the “American anti-slavery war” was a catalyst of empowerment “for the working classes.”[7]

It was clear that the decision-makers in England and France knew the war was being fought over slavery, an institution both countries had ended in 1833 and 1848, respectively. The conundrum they then faced was how to obtain cotton from a slave nation. The English newspaper, Reynolds Weekly, rationalized that as long as the North did not openly fight against slavery, Britons faced no moral dilemma; therefore, if the Union wanted to gain English sympathies, “they must abolish slavery.”[8] This idea not only boasted ideological importance but had practical implications, as well.

President Lincoln had no authority under the Constitution to end slavery. Congress; however, took small steps in that direction as early as August 1861 by passing an act that allowed for the seizure of all Confederate property, including slaves. Additionally, slaves who escaped to Union held territories and forts did not have to be returned to their owners and were subsequently labeled, “contrabands.” Further acts were passed that ended slavery in Washington, D.C., forbade Union officers to return slaves who had escaped the South, and authorized the active confiscation of slaves from owners.

The implications to the South were felt most significantly in the economic and logistic realms. Slaves were essentially part of the support system for the southern war machine. In the military they acted as laborers, cooks, and in other auxiliary functions. On the home front, slaves were practically the only males to work the land. The elimination of slave labor resulted in a stark decrease in crop production thus affecting the economic market; not to mention the ability to feed the population. In the military units, for each slave that was lost, an infantry soldier had to be pulled from combat to perform his duties.

President Lincoln became increasingly aware of the importance of removing slaves from the southern war effort and the impact of emancipation in relation to England and France. By the summer of 1862, he was eager to issue a proclamation but was cautioned against doing so by Secretary of State William H. Seward. Secretary Seward cautioned Lincoln that if he issued a proclamation without military support in the form of a victory, it may be seen as “the last measure of an exhausted government.”[9] Seward was correct and Lincoln waited for a military victory in the East.

Why did Lee invade Maryland?

General Robert E. Lee, 1863

General Lee was a brilliant military tactician and strategist. By invading the North, Lee hoped to strike a fatal blow to the Union war effort by influencing the Border States in favor of the South, possibly capturing Washington, D.C., and gaining foreign recognition. In obtaining an acknowledgment from foreign powers as an independent nation, the CSA could then conduct foreign trade, negotiate militarily, and especially put great pressure on the United States to end the war.[10]

Although the South was doing well in the eastern theater and still maintained more than 85% of initially held Confederate territory, despite losses in the western theater of the war, Lee knew that a war of attrition meant certain defeat for the Confederacy. War resources were overwhelmingly in favor of the North. The population in the northern states was 22 million compared to the 9 million in the South; 3.5 million of which were chattel slaves. The northern states boasted 1100,000 factories while the agrarian southern states house just 18,000. The Union enjoyed a 32:1 ratio in firearms and $1.5 billion dollars from the production of goods compared to the $155 million produced in the Confederacy.[11]

Lee and his advisors were familiar with the resources available to the North and knew that swift action and a decisive blow afforded the CSA the best chance of victory. On September 17, 1862, Lee and McClellan faced off in Sharpsburg and essentially fought to a stalemate. Lee was forced to retreat south yet McClellan gave no chase thus enabling the Army of Northern Virginia to successfully retreat and regroup in the South.

What was the Aftermath of Antietam?

Lee did not strike the decisive blow for which he had hoped and the Union Army under McClellan made no southerly progress. Land was not lost that day but an extraordinary number of lives were. In just one day, the total number of killed or mortally wounded was between 6,300 and 6,500. An additional 15,000 men were wounded. In this one day, the casualties numbered greater than 21,000 which is more than the number of American casualties on the Normandy beaches on June 6, 1944; D-Day.

Further, the combined casualties of the War of 1812, the Mexican-American War, the Spanish-American War, and the Indian wars of the 19th century yielded fewer casualties.[12] A lieutenant from the 57th New York who was on burial detail at Antietam saw the dead “in every state of mutilation, sans arms, sans legs, heads, and intestines, and in greater number than on any field we have seen before.”[13]

The battle ended in a stalemate and the loss of life was appalling yet the day offered a turning point in the war and in American history. Due to Lee’s retreat, the politicians of the North declared Antietam a victory thus providing the impetus President Lincoln needed to issue the Emancipation Proclamation. This document did not “free the slaves,” as is so often misunderstood, but it marked the decline of the CSA. The government of the South was given an ultimatum by Lincoln. He issued the preliminary Proclamation five days after Antietam with the stipulation that if the Confederacy did not surrender their arms and reunite with the nation before January 1, 1863, the Proclamation would become the permanent law of the land.


The war waged on long after 1863 began and the Emancipation Proclamation became law. The positive wartime ramifications were numerous: exacerbation of the manpower shortage in the South; black troops fighting in the North; the refusal of England and France to recognize the CSA while they fought a nation attempting to end slavery. The humane and ideological consequences need not be discussed as they are quite evident.

The victory claimed by the North in the Battle of Antietam convinced England and France to remain neutral regardless of their reliance on cotton and prompted the issuance of the Emancipation Proclamation, without which the outcome of the war and history itself may have been permanently altered. The importance of this battle was not lost on Karl Marx, who wrote just one month hence that this battle “has decided the fate of the American Civil war.”[14]


  1. James McPherson, Crossroads of Freedom: Antietam, The Battle That Changed the Course of the Civil War (New York: Oxford University Press, 2002), 11.
  2. McPherson, Crossroads of Freedom, 16-24.
  3. McPherson, Crossroads of Freedom, 35.
  4. James McPherson, Battle Cry of Freedom: The Civil War Era (New York: Oxford University Press, 1988), 548.
  5. Henry Adams to Charles Francis Adams, Jr., May 8, 1862, in Worthington C. Ford, ed., A Cycle of Adams Letters 1861-1865, 2 vols. (Boston, 1920), 1:139.
  6. Belle B. Sideman and Lillian Friedman, eds., Europe Looks at the Civil War (New York, 1960), 117-18.
  7. Saul K. Padover, ed. and trans., Karl Marx on America and the Civil War (New York, 1972), 263-64.
  8. Reynolds Weekly, quoted in McPherson, Battle Cry, 553.
  9. Francis B. Carpenter, Six Months at the Whitehouse with Abraham Lincoln (New York, 1866), 22.
  10. McPherson, Crossroads of Freedom, 37.
  11. Eric Foner, Give Me Liberty! An American History, 2nd ed. (New York: W.W. Norton & Company, 2009), 1:486.
  12. McPherson, Crossroads of Freedom, 3.
  13. Josiah Favill, Diary of a Young Officer, quoted in McPherson, Crossroads of Freedom, 4.
  14. Padover, Karl Marx, 220.

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