Saturday, September 17, marks the 160th anniversary of the 1862 battle that remains the bloodiest single day in American history. On that date, nearly 6,000 Americans were killed and another 19,000 wounded or went missing on a compact field of carnage near Sharpsburg, Maryland on the banks of Antietam Creek.
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 the Union. 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 Rebel 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. After a close call at Shiloh, Grant had captured the critical railroad junction at Corinth, Mississippi. New Orleans had already fallen in the early spring, and in short order, the only stretch of the Mississippi the Confederates controlled was 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 effort 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 Johnston, who, after being seriously wounded, was replaced by President Jefferson Davis’ military adviser, Robert E. Lee.
Lee had long recognized the key to Confederate strategy: 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 strategic turning movements 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.
Accordingly, Lee immediately went on the offensive, attacking McClellan on the banks of the Chickahominy River 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 River, he detached one of his two corps under Thomas “Stonewall” Jackson to confront a new threat, 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. As Joseph Harsh argued in his study of the Maryland campaign, Confederate Tide Rising: Robert E. Lee and the Making of Southern Strategy, “the single tapestry” of the campaign “[stretching] from Beaver Dam Creek on June 26 to Shepherdstown on September 20 . . . represented a calculated attempt to restore Confederate resources, to demoralize the North, and to win the war in the summer of 1862.”
Lee believed “the Confederacy had reached the fulcrum of its fate” and judged that “it was necessary to risk all because a similar opportunity most likely would never come again.” Lee’s strategic perception was correct: “Lee’s strategy to demoralize the North, and for the most part his execution of that strategy gave the Confederacy the best chance it would ever have to win its independence.”
The time now appeared to be “propitious,” as Lee wrote to Davis, to invade Maryland. Not only had Lee’s efforts during the Seven Days and especially at Second Manassas been crowned with success, but also Lee 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 manpower reservoir. Meanwhile, Confederate armies in the West were on the move toward Ohio. As Harsh remarked, the Confederacy was indeed at flood tide. Without success, the tide would only recede.
The goals of Lee’s Maryland campaign included relieving Virginia from the scourge of foraging armies by subsisting for as long as possible off enemy resources; enticing Maryland into secession; strengthening the Northern peace party in the upcoming congressional elections; and encouraging recognition by Great Britain and France. But Lee aimed at something more: to change the very 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.
As Harsh observes, when Lee crossed into Maryland on September 4, “Lee’s army was an instrument of sufficient strength and mettle to justify crossing the Potomac. From the 14th onward, however, his unrelenting demands blunted the weapon in his hands and reduced its power.” The main problem was Lee’s decision to capture Harper’s Ferry, believing that the garrison there presented a threat to his lines of communication. To do so, Lee had to divide his force—this in itself was never a problem for Lee—but he now did so in ignorance of McClellan’s location.
Lee dispatched Jackson to capture Harper’s Ferry, assuming the garrison would either flee or quickly capitulate. Meanwhile, he sent Longstreet to Boonsboro to guard against what he expected to be a characteristically cautious approach by McClellan. But the garrison at Harper’s 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.
The conventional wisdom has usually attributed the rapidity of McClellan’s advance to the “Lost Dispatch,” a copy of Lee’s Special Order 191 that fell into Union hands. According to this view, McClellan now knew Lee’s plan and the disposition of his divided army. But the importance of S.O. 191 is overstated. The fact is that McClellan was already moving “more rapidly than convenient” against Lee’s rear before the discovery of the order. Lee was largely unaware of McClellan’s progress because of the failure of Stuart’s cavalry to provide the necessary intelligence—he was genuinely surprised when McClellan reached Frederick on September 12. Additionally, S. O. 191 gave McClellan no information about the strength of Lee’s army or its constituent parts.
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. Harper’s 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 took up a position near the little town of Sharpsburg.
Even as late as the early afternoon of September 16, Lee fully intended to renew his offensive by drawing McClellan to the west where he could gain an advantage by maneuver. He had paused at Sharpsburg not to fight but to permit his army to reunite after the surrender of Harper’s Ferry. Only after Stuart reported that McClellan’s troops were crossing the upper Antietam did he grudgingly accept a defensive battle, his maneuver option now foreclosed.
But even with a reunited army, 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 his soldiers. As a result, when McClellan unleashed his attack at dawn on September 17, Lee’s army was only half the strength of McClellan’s (38,000 to 76,000).
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 Federals surged forward only to be driven back by desperate Confederate counterattacks. When Lee asked John Bell Hood where his division was, the latter 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 running along a sunken road, one Union division was able to flank it, delivering a deadly enfilading 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.
Meanwhile, the action now shifted to the Union left, where Ambrose Burnside’s corps was stymied in an attempt to cross a bridge over Antietam Creek (the stream was fordable further to the south) by a small detachment of Rebels. Finally in the middle of the afternoon, Burnside carried the bridge and was pressing the Confederate right back toward Sharpsburg. On the cusp of victory, Burnside was struck on the flank by A.P. Hill’s division returning from Harper’s Ferry. The Confederate position was held—barely.
Lee remained at Sharpsburg on the 18th, but McClellan refused to renew the battle. Although his casualties were heavy (12,400 dead, wounded, and missing), Lee’s were, of course, proportionately heavier (10,300). 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.
In his memoirs, Longstreet wrote that “at Sharpsburg was sprung the keystone of the arch upon which the Confederate cause rested.” Longstreet was correct. Antietam was a tactical draw but a Union strategic victory. For the Confederacy, it represented the culmination of the Confederacy’s maximum effort. Lee would win other victories and indeed, would invade the North again. But this time instead of operating in conjunction with Confederate armies in the West, he would be trying to offset reverses at Vicksburg and Chattanooga. The Battle of Antietam/Sharpsburg also 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.
For the Union, Antietam, although a draw, provided an opportunity for President Abraham Lincoln to reverse Union fortunes just as surely as Lee had earlier 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 for the Union, 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 blacks, 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 blacks would have positioned themselves to eventually achieve full citizenship.