Monday, September 17, marks the sesquicentennial of the 1862 battle that remains the bloodiest day in American history. On that day, nearly 6,000 Americans were killed and another 19,000 wounded or went missing on a compact field of carnage near Sharpsburg, Md.
But the Battle of Antietam is consequential in several other ways as well. First, it arguably marks the true high water mark of the Confederacy. Second, it made possible the policy change that Abraham Lincoln would need to win the war.
Events in the Virginia theater during the spring and summer of 1862 marked a reversal of fortune for both the Union and the Confederacy. Casual students of the Civil War often do not realize how bad things were for the Confederacy in the spring of that year. A Confederate army had won a stunning victory at Manassas in July of 1861, but then southern fortunes faded.
In the west, Union armies under Henry Halleck and Ulysses S. Grant had used the Tennessee River to drive deep into western Tennessee and northern Mississippi, capturing the critical railroad junction at Corinth. New Orleans had already fallen in the early spring, and in short order, the only stretch of the Mississippi that the Confederates controlled lay between Vicksburg and Port Hudson.
Things were not much better in the East. A large Union army commanded by George McClellan had reached the outskirts of Richmond by the end of May, impelling the Confederate commander, Joseph E. Johnston, to attack, which he did on May 31 at Seven Pines/Fair Oaks. The uncoordinated attack soon bogged down and the rebels were forced to retreat. Casualties on both sides were heavy, but the most consequential casualty on either side was Johnson, who was replaced by President Jefferson Davis’s military adviser, Robert E. Lee.
Lee recognized that the key to Confederate strategy was the fact that, as long as the Union remained determined to subdue the South, the Confederacy could not win its independence. The northern population had to be demoralized in order to force the Union to abandon the war. A defensive strategy would not work because the Confederacy lacked the necessary strategic depth and because reliance on the defensive played to northern strengths in engineering, artillery, and naval assets, minimizing Union losses and allowing the North to succeed with far less than full mobilization.
Lee aimed to change the character of the war as things stood in the spring of 1862, employing the strategic turning movement and open-field maneuvering by infantry and cavalry to neutralize the Union’s aforementioned advantages. For Lee, maneuver was not an end in itself but the means to gain an advantage in order to attack the enemy and inflict heavy losses. Only in this manner, Lee believed, could the population of the North be convinced that a costly and interminable struggle lay ahead if the South were not granted its independence.
Thus Lee immediately went on the offensive, attacking McClellan on the banks of the Chickahominy on June 26. In a series of turning movements during the Seven Days campaign, Lee drove McClellan back from Richmond. Although Union forces prevailed in most of the tactical engagements during this operation, the strategic result was that Richmond was spared the siege that would have inevitably led to its fall.
Once Lee had pushed McClellan back to the James, he detached one corps under Stonewall Jackson to confront John Pope’s Army of Virginia to the north. Even before he was certain that McClellan was withdrawing from the Peninsula, Lee dispatched the other corps under James Longstreet to gain Pope’s rear, then unleashed his entire army in a furious assault against Pope at Second Manassas. Although Pope escaped destruction, the operation ended in a rout that demoralized the federal government and its army, placing Lee as close to Washington as McClellan had been to Richmond only two months earlier.
Lee now contemplated an incursion into Maryland as the logical follow-up to the smashing victory at Second Manassas. He intended to inflict another humiliating defeat on the demoralized Union forces, this time in western Maryland.
The time was ripe. Not only had Lee’s efforts up to now met success, but he also knew that with the April Conscription Act, the Confederacy had exerted its maximum effort to bring troops into the field while the North had barely tapped its reserves of manpower. Meanwhile, the Confederate armies in the West were on the move toward the Ohio.
The Battle of Antietam/Sharpsburg was a tactical draw. McClellan deployed his troops piecemeal, permitting Lee to hold on by his teeth. Time after time, Lee, badly outnumbered and with his back to the Potomac, was able to avert disaster by shifting his forces from one part of the field to another. For some reason, McClellan did not commit his reserve, which may well have crushed the Confederates. That the battle ended as a tactical draw is seen as a tribute to Lee’s generalship.
But it marked the failure of Lee’s preferred strategy. For the Confederacy, Antietam marked flood tide. As events were to prove, having failed, the South would only recede.
On the other hand, the battle, although a draw, provided an opportunity for President Abraham Lincoln to reverse Union fortunes just as surely as Lee had reversed those of the Confederacy. Thus, after Lee’s invasion of Maryland was turned back, Lincoln issued a preliminary Emancipation Proclamation on September 22, which gave the Confederates 100 days to submit to the Union or face the prospect of immediate emancipation of its slaves. The time had come, Lincoln wrote to Cuthbert Bullitt, to stop waging war “with elder-stalk squirts, charged with rose water.”
Southern Unionists, loyal slave-holders, and Democrats charged that Lincoln was “revolutionizing” the war by issuing his proclamation. Lincoln did not disagree, admitting that once the proclamation took effect, “the character of the war will be changed. It will be one of subjugation and extermination.”
From a military standpoint, emancipation was a war measure designed to attack the southern economy directly. As Halleck explained to Grant, “The character of the war has very much changed within the last year. There is now no possible hope of reconciliation. . . . We must conquer the rebels or be conquered by them. . . . Every slave withdrawn from the enemy is the equivalent of a white man put hors de combat.”
Emancipation had the effect of transferring labor from the South to the North, increasing the fighting potential of Union armies while decreasing that of the Confederate armies. As Gideon Welles, Lincoln’s secretary of the navy, recalled, the president called emancipation “a military necessity, absolutely essential to the preservation of the Union. We must free the slaves or be ourselves subdued. The slaves were undeniably an element of strength to those who had their service, and we must decide whether that element should be with us or against us.”
Militarily, the Emancipation Proclamation opened the way to the next logical step in this process of weakening the South while strengthening the North: enrolling blacks as soldiers in the Union army. The manpower boost to the Union was substantial. But while the material contribution to the Union victory by African Americans, both free men and former slaves, was substantial, their participation in the war to achieve their own liberty was important for its own sake. Without their participation, the war to save the Union “as it was” could not have been transformed into a war to save the Union “as it should be,” i.e., without slavery, and it is unlikely that African Americans could ever have achieved full citizenship and equality in the United States.
— Mackubin Thomas Owens is a professor at the Naval War College and editor of Orbis, the journal of the Foreign Policy Research Institute. He is a Marine-infantry veteran of the Vietnam War.