The Battle of Antietam was a key turning point in the American Civil War and American history. In short, it turned back Robert E. Lee’s first campaign north of the Potomac River and led to the issuance of the Preliminary—and then, final—Emancipation Proclamation. However, many historians and students of the war refer to the battle fought on September 17, 1862 as a draw. Or, they throw the Army of the Potomac a bone and say while it was tactically a draw, the battle and campaign that it climaxed were a strategic Union victory, throwing back Lee’s first invasion of the North.
A drawn battle implies that, at the end of the battle, neither side held a clear advantage over the other. Instead, after the fighting concluded on September 17, 1862, the Army of the Potomac’s gains after the day’s actions severely restricted the Army of Northern Virginia’s options, giving the Federal army the upper hand in the Maryland Campaign.
Certainly, in the eyes of many visitors to Antietam National Battlefield, the belief that the Army of the Potomac and its commander, Maj. Gen. George B. McClellan, could have destroyed or at least damaged Lee’s Army of Northern Virginia far more than it did or destroy it does not help lift the Federals’ success above anything more than a draw. Instead, three days after the battle, McClellan wrote his wife, “Our victory was complete & the disorganized rebel army has rapidly returned to Virginia.” Additionally, President Abraham Lincoln’s post-battle frustration with McClellan’s failure to move his army into Virginia until six weeks after the battle seems to indicate the President was displeased with the battle’s outcome. If Lincoln held this belief, the common perception goes, it is difficult to see how Antietam could be anything but a draw.
Lee knew a tactical defeat when he saw one. In fact, he suffered one three days prior at South Mountain. Even before he learned of what befell portions of his army at Crampton’s Gap, Lee told one of his commanders, “The day has gone against us and this army will go by Sharpsburg and cross the [Potomac] river” into Virginia. “It is necessary for you to abandon your position to-night.” For Lee, recrossing the Potomac River into Virginia was the last thing he wanted to do. It would mark the end of his campaign into Maryland. Plus, should he continue to hope that he could recross that river a third time in an attempt to resume his campaign, he would now have to do so with an enemy force along the river, making such an effort a desperate one. Returning to Virginia was Lee’s last option in his campaign playbook, but on the night of September 14, he believed he had no other play to call.
Lee’s withdrawal from South Mountain that night was “a daunting task,” in the words of campaign historian Joseph L. Harsh. “We had a bad night on the mountain,” admitted Moxley Sorrel, one of Maj. Gen. James Longstreet’s staff officers. In their haste to withdraw, the Army of Northern Virginia abandoned its dead and wounded on the slopes of South Mountain. A hasty, unplanned, nighttime retreat with unburied dead and uncared wounded left behind signaled a tactical victory for the Army of the Potomac at South Mountain.
The Confederate army’s retreat to Virginia would have continued had it not been for a few events that happened overnight and by the early morning of September 15. First, Lee realized his movement across the Potomac River would endanger the two divisions under Maj. Gen. Lafayette McLaws’ command in Pleasant Valley that was hemmed in between two mountain ranges, a river at his back, and two enemy forces in his front and rear. Second, Lee received a note from Maj. Gen. “Stonewall” Jackson that Harpers Ferry and its Union garrison (which stood in McLaws’ rear) were likely to capitulate soon, which would allow Lee to reunite the separated portions of his army and try to resurrect his campaign. Lastly, Lee examined the terrain around Sharpsburg, Maryland. He liked what he saw.
Despite its offensive nature, Lee fought the Maryland Campaign brilliantly from a defensive perspective. In every phase of the campaign, Lee placed natural barriers between his army and the enemy. First, he crossed the Potomac River into Maryland in early September while most of the Federal army was south of that river in Virginia. Then, after occupying Frederick, the Army of Northern Virginia held “the line of the Monocacy,” keeping this central Maryland river between Lee’s force and any Federals approaching from the direction of Washington, DC. Once Lee divided his army to rid the Shenandoah Valley of Union garrisons at Martinsburg and Harpers Ferry, his scattered forces shielded themselves behind two mountain ranges west of Frederick: Catoctin and South mountains. Lee’s withdrawal from South Mountain on the evening of September 14 deprived him of his third defensive barrier. He planned to use the Potomac River as the barrier behind which he would gather his disparate army until he received word of the imminent surrender of Harpers Ferry and until he found another strong natural barrier to place between himself and the victorious enemy: Antietam Creek.
The creek was formidable enough that it could only be crossed at five points in the immediate vicinity of the Antietam battlefield. From north to south, these crossings were the Upper Bridge, Pry’s Ford, the Middle Bridge, the Lower (Burnside) Bridge, and Snavely’s Ford.
As Lee’s army gathered on the high ground west of the creek on September 15-16, Lee formed his men for battle. On his left, due to his small force at that time, he set his main line back from the two upper crossings, the Upper Bridge and Pry’s Ford. In his center posted on Cemetery Hill, Lee’s men overlooked the creek from a distance, though his artillery was close enough to make any crossing of the Middle Bridge hazardous. Infantry was also posted to rake the flanks of any troops crossing the bridge. Lee’s right flank rested directly on the creek at the Lower Bridge and Snavely’s Ford. While Lee gifted McClellan three of the five major crossing points before the battle even commenced, the Confederates still held enough of the bridges and fords over the creek to make it a barrier that the Federals had to cross to drive Lee out of Maryland and back into Virginia.
In order for McClellan to do that, he had to determine what the best avenue of advance was to pry Lee from his line on the heights around Sharpsburg. Of the crossings available to him, the Middle Bridge provided the largest potential reward. It was the shortest, most direct route to Lee’s army. Lee’s defensive position, however, ensured that attacking his center would be no easy task. On Lee’s right, McClellan’s men would have to fight to cross the creek before attacking the main Confederate line. Thus, McClellan looked to Lee’s left to strike the blow that would drive the Army of Northern Virginia out of Maryland.
Utilizing two crossings that Lee left uncovered—the Upper Bridge and Pry’s Ford—McClellan placed approximately 9,000 men of Maj. Gen. Joseph Hooker’s First Corps on the northern end of Lee’s line. It was then that McClellan realized the peril of fighting along Antietam Creek and Lee realized the potential for success. Despite his aggressive tendencies, Hooker feared that the enemy, who outnumbered his small force on the west side of the creek, “would eat me up.” With the gift of hindsight, Lee’s second-in-command, Maj. Gen. Longstreet, equally recognized Hooker’s precarious position. Regarding September 16 and Hooker’s movement, Longstreet wrote:
If Jackson could have been put into this fight, and also the brigades under J.G. Walker, Hooker’s command could have been fought out, if not crushed, before the afternoon went out. He was beyond support for the day, and the posting along the Antietam was such—we will soon see—as to prevent effective diversion in his favor.
Hooker’s fear and Longstreet’s prediction never came to fruition, but they speak to the importance of the creek in Lee’s battle plan. Because McClellan did not control all of the crossings of the creek, his army would be forced to divide itself as it moved to the stream’s west side to assault Lee’s line. (The Battle of Antietam was not the first time a body of water worked in Lee’s favor in such a manner. His plan at the onset of the Seven Days’ Campaign was to hit McClellan’s separated right flank on the north side of the Chickahominy. Lee later tried to use the North Anna River in May 1864 to once again divide the Army of the Potomac and help even the numerical odds so that Lee could bring balanced or larger numbers to bear on his enemy at the point of attack.)
To address Hooker’s concerns, McClellan eventually reinforced him with roughly 7,000 men of the Twelfth Corps. Hooker’s men began their attack the next morning. Their objective was one of the key terrain features on the Antietam battlefield: the Dunker Church Plateau.
Aside from controlling two of the five main crossing points of Antietam Creek, Lee also controlled two other key terrain features on the Antietam battlefield when the sun rose on September 17. Lee centered his line on Cemetery Hill (site of Antietam National Cemetery), which rises nearly 200 feet above the creek one mile to the east. The Confederate army anchored its left in front of the Dunker Church Plateau, another prominent eminence towering above the stream. This latter terrain feature was Hooker’s objective on the morning of the 17th.
After the all-day Battle of Antietam, the only key terrain Lee still held onto was Cemetery Hill. On his left, Federals held the Dunker Church Plateau, which, by Hooker’s estimation, “commanded the position taken by the enemy on his retreat from South Mountain.” Similarly, on the southern end of the field, Maj. Gen. Ambrose Burnside’s Ninth Corps forced the two creek crossings there (the Lower Bridge and Snavely’s Ford), giving McClellan control of the creek itself and depriving Lee of another natural barrier.
The Army of the Potomac’s gains made on September 17 were not tremendous, but they severely limited Lee’s options. Prior to these Federal advances, the road network around Sharpsburg gave Lee flexibility about where he could maneuver his army. Enemy positions sealed those avenues of advance on September 16. Hooker’s movement west across the creek on September 16 and the subsequent capture of the Dunker Church Plateau contained Lee’s army from the north, cutting off any use he might have had of the Hagerstown Turnpike. On at least three occasions on September 17, Lee attempted to drive the Federals on his left flank back. He failed each time. A reconnaissance by “Stonewall” Jackson and Col. Stephen D. Lee on the morning of September 18 confirmed that a fourth attempt would not succeed. When Col. Lee reported his findings to the commanding general, he recalled that he observed “a shade come over General Lee’s face.” Lee had only two other options available to him on September 18: to stand and fight one day after his army suffered 10,316 casualties—27.6% of its strength—or withdraw into Virginia. Neither option was a good one. The Federal capture of the Dunker Church Plateau and McClellan’s control of all the creek’s crossing points forced Lee into this no-win situation. Lee was now faced with a difficult situation in which he could no longer use the creek to aid in his battle plans, either offensively or defensively.
Elsewhere along the line, Lee found no opportunities to attack the Federals. With all five crossing points in their possession, McClellan’s army stood in a near-continuous line four miles long. No longer could Lee attempt to strike at a divided portion of the Army of the Potomac as Longstreet suggested. With no good options, Lee ordered his army to leave a battlefield because of Federal tactical gains for the second time in four days. This move placed the Potomac River between Lee and the enemy, making it the final defensive barrier that he utilized in the campaign. During these two rearward movements, McClellan’s army swept up “thirteen guns and thirty-nine colors, more than 15,000 stand of small-arms, and more than 6,000 prisoners.”
In the end, the Army of the Potomac’s tactical successes on September 17, 1862 were enough to accomplish that army’s campaign objectives of driving the enemy out of Maryland. Those successes were even enough to satisfy President Lincoln. On September 22, Lincoln called his Cabinet together to announce that now was the time to announce the Preliminary Emancipation Proclamation. That document sat in Lincoln’s desk for the last two months as he waited for a victory that would allow him to announce it from a position of strength. The President explained why the proper time to publicly declare this war-changing measure was after the victory at Antietam. He admitted now was not the perfect time. “I wish it were a better time,” he said. “I wish that we were in a better condition. The action of the army against the rebels has not been quite what I should have best liked. But,” he continued, the enemy “have been driven out of Maryland, and Pennsylvania is no longer in danger of invasion. When the rebel army was at Frederick, I determined, as soon as it should be driven out of Maryland, to issue a Proclamation of Emancipation such as I thought most likely to be useful.” He did not share his precondition for victory in the campaign with anyone. He did vow, though, “The rebel army is now driven out, and I am going to fulfil that promise.”
Those same tactical successes that allowed the Army of the Potomac to achieve its ultimate campaign objective—driving the enemy out of Maryland—deprived Lee of the ability to attain his: bringing the Federal army to battle and defeating it north of the Potomac River. Lee had options available to him to keep his objective in sight before September 17. Following the bloodiest single day of battle in American history, Lee’s options were restricted to two bad ones. The Battle of Antietam presented Lee with these bad options. Neither option left to Lee the potential for a successful continuation of the campaign north of the Potomac River. This in itself underscores how the Battle of Antietam was, tactically, a Federal victory. The Federals’ tactical success on September 17 ensured the Maryland Campaign was a victory for the United States.
 Sears, ed., The Civil War Papers of George B. McClellan: Selected Correspondence 1860-1865, 473.
 OR, vol. 51, pt. 2, 618.
 Harsh, Taken at the Flood, 290.
 OR, vol. 19, pt. 1, 28.
 OR, vol. 19, pt. 2, 596.
 OR, vol. 19, pt. 1, 217.
 Longstreet, From Manassas to Appomattox, 237.
 OR, vol. 19, pt. 1, 218.
 Harsh, Taken at the Flood, 443.
 OR, vol. 19, pt. 1, 33.
 David Donald, ed., Inside Lincoln’s Cabinet: The Civil War Diaries of Salmon P. Chase (New York: Longmans, Green and Co., 1954), 150.