Maryland campaign
The Maryland campaign occurred September 4–20, 1862, during the American Civil War. The campaign was Confederate General Robert E. Lee's first invasion of the North. It was repulsed by the Army of the Potomac under Maj. Gen. George B. McClellan, who moved to intercept Lee and his Army of Northern Virginia and eventually attacked it near Sharpsburg, Maryland. The resulting Battle of Antietam was the bloodiest day of battle in American history.
Following his victory in the northern Virginia campaign, Lee moved north with 55,000 men through the Shenandoah Valley starting on September 4, 1862. His objective was to resupply his army outside of the war-torn Virginia theater and to damage Northern morale in anticipation of the November elections. He undertook the risky maneuver of splitting his army so that he could continue north into Maryland while simultaneously capturing the Federal garrison and arsenal at Harpers Ferry. McClellan accidentally found a copy of Lee's orders to his subordinate commanders and planned to isolate and defeat the separated portions of Lee's army.
While Confederate Maj. Gen. Stonewall Jackson surrounded, bombarded, and captured Harpers Ferry, McClellan's army of 102,000 men attempted to move quickly through the South Mountain passes that separated him from Lee. The Battle of South Mountain on September 14 delayed McClellan's advance and allowed Lee sufficient time to concentrate most of his army at Sharpsburg. The Battle of Antietam on September 17 was the bloodiest day in American military history with over 22,000 casualties. Lee, outnumbered two to one, moved his defensive forces to parry each offensive blow, but McClellan never deployed all of the reserves of his army to capitalize on localized successes and destroy the Confederates. On September 18, Lee ordered a withdrawal across the Potomac and on September 19–20, fights by Lee's rearguard at Shepherdstown ended the campaign.
Although Antietam was a tactical draw, it meant the strategy behind Lee's Maryland campaign had failed. President Abraham Lincoln used this Union victory as the justification for announcing his Emancipation Proclamation, which effectively ended any threat of European support for the Confederacy.
Background
Military situation
The year 1862 started out well for Union forces in the Eastern Theater. George B. McClellan's Army of the Potomac had invaded the Virginia Peninsula during the Peninsula Campaign and by June stood only a few miles outside the Confederate capital at Richmond. However, when Robert E. Lee assumed command of the Army of Northern Virginia on June 1, fortunes reversed. Lee attacked McClellan aggressively at the end of June in the Seven Days Battles; McClellan lost his nerve, and his army retreated down the Peninsula. In July, Lee then conducted the northern Virginia campaign in which he outmaneuvered and defeated Maj. Gen. John Pope and his Army of Virginia, most significantly at the Second Battle of Bull Run, before McClellan's corps could reinforce Pope. Lee's Maryland campaign can be considered the concluding part of a logically connected, three-campaign, summer offensive against Federal forces in the Eastern Theater.The Confederates had suffered significant manpower losses in the wake of the summer campaigns. Nevertheless, Lee decided his army was ready for a great challenge: an invasion of the North. His goal was to reach the major Northern states of Maryland and Pennsylvania, and cut off the Baltimore and Ohio Railroad line that supplied Washington, D.C. His movements would threaten Washington, D.C., and Baltimore, so as to "annoy and harass the enemy."
Several motives led to Lee's decision to launch an invasion. First, he needed to supply his army and knew the farms of the North had been untouched by war, unlike those in Virginia. Moving the war northward would relieve pressure on Virginia. Second was the issue of Northern morale. Lee knew the Confederacy did not have to win the war by defeating the North militarily; it merely needed to make the Northern populace and government unwilling to continue the fight. With the Congressional elections of 1862 approaching in November, Lee believed that an invading army playing havoc inside the North could tip the balance of Congress to the Democratic Party, which might force Abraham Lincoln to negotiate an end to the war. He told Confederate President Jefferson Davis in a letter of September 3 that the enemy was "much weakened and demoralized."
There were secondary reasons as well. The Confederate invasion might be able to incite an uprising in Maryland, especially given that it was a slave-holding state and many of its citizens held a sympathetic stance toward the South. Some Confederate politicians, including Jefferson Davis, believed the prospect of foreign recognition for the Confederacy would be made stronger by a military victory on Northern soil, but there is no evidence that Lee thought the South should base its military plans on this possibility. Nevertheless, the news of the victory at Second Bull Run and the start of Lee's invasion caused considerable diplomatic activity between the Confederate States and France and the United Kingdom. Additionally, generals Braxton Bragg and Edmund Kirby Smith in the Western Theatre outmaneuvered Don Carlos Buell to reach the border state of Kentucky from eastern Tennessee through the Battle of Richmond which coincided with Confederate victories in the East.
After the defeat of Pope at Second Bull Run, President Lincoln reluctantly returned to the man who had mended a broken army before—George B. McClellan, who had done it after the Union defeat at the First Battle of Bull Run. He knew that McClellan was a strong organizer and a skilled trainer of troops, able to recombine the units of Pope's army with the Army of the Potomac faster than anyone, and there was no other viable choice for the job except Burnside, who was asked and declined command of the army. On September 2, Lincoln named McClellan to command "the fortifications of Washington, and all the troops for the defense of the capital." The appointment was controversial in the Cabinet, a majority of whom signed a petition declaring to the president "our deliberate opinion that, at this time, it is not safe to entrust to Major General McClellan the command of any Army of the United States." The president admitted that it was like "curing the bite with the hair of the dog." But Lincoln told his secretary, John Hay, "We must use what tools we have. There is no man in the Army who can man these fortifications and lick these troops of ours into shape half as well as he. If he can't fight himself, he excels in making others ready to fight."
Opposing forces
Union
Maj. Gen. George B. McClellan's Army of the Potomac, bolstered by units absorbed from John Pope's Army of Virginia, included six infantry corps, about 102,000 men.- The I Corps, under Maj. Gen. Joseph Hooker, consisted of the divisions of Brig. Gens. Rufus King, James B. Ricketts, and George G. Meade.
- The II Corps, under Maj. Gen. Edwin V. Sumner, consisted of the divisions of Maj. Gens. Israel B. Richardson and John Sedgwick, and Brig. Gen. William H. French.
- The V Corps, under Maj. Gen. Fitz John Porter, consisted of the divisions of Maj. Gen. George W. Morell, Brig. Gen. George Sykes, and Brig. Gen. Andrew A. Humphreys.
- The VI Corps, under Maj. Gen. William B. Franklin, consisted of the divisions of Maj. Gens. Henry W. Slocum and William F. "Baldy" Smith, and a division from the IV Corps under Maj. Gen. Darius N. Couch.
- The IX Corps, under Maj. Gen. Ambrose E. Burnside, consisted of the divisions of Brig. Gens. Orlando B. Willcox, Samuel D. Sturgis, and Isaac P. Rodman, and the Kanawha Division, under Brig. Gen. Jacob D. Cox.
- The XII Corps, under Maj. Gen. Joseph K. Mansfield, consisted of the divisions of Brig. Gens. Alpheus S. Williams and George S. Greene, and the cavalry division of Brig. Gen. Alfred Pleasonton.
The army that McClellan took into Maryland was not an entirely cohesive or battle-ready fighting force. At its core were the Peninsula veterans of the II, V, and VI Corps, but a large portion of the army were untested rookie regiments or troops who had never fought as part of the Army of the Potomac. Some of the rookies had never even loaded their muskets, and others were unknowingly armed with defective weapons.
The "core" Army of the Potomac, the II, III, V, and VI Corps, which had served through the Peninsula Campaign, were the easiest ones to get ready for action. In addition there were the three corps that had comprised Pope's army. Aside from the Pennsylvania Reserves, which had born the brunt of action in the Seven Days Battles, none of these troops had served under McClellan before, all had been poorly led, and did not have much record of battlefield success. The two divisions of Burnside's IX Corps were also new to McClellan, but they had served capably in North Carolina early in the year. The IX Corps was also being joined by Brig. Gen Jacob D. Cox's "Kanawah" division from West Virginia, new to McClellan as well. These troops had seen no major action so far and were essentially green.
The I Corps had excellent troops; as mentioned above the Pennsylvania Reserves had been in the thick of the Seven Days Battles and all three divisions were heavily engaged at Second Bull Run. McDowell however had been written off as a loser, he was despised by his own troops and would not hold a command in the Civil War again. McClellan's first choice to lead the I Corps was his friend and intimate Jesse Reno, then having operational command of the IX Corps but instead the position went to Joe Hooker, considered a more experienced officer.
The XII Corps under Nathaniel Banks had a poor reputation; it had been badly defeated by "Stonewall" Jackson's troops during the Valley Campaign in spring, had fought poorly at Cedar Mountain, and Pope held the corps and Banks in such low regard that he kept them away from the Second Bull Run battlefield. Banks was dropped from command of the XII Corps and eventually sent to Louisiana. Brig. Gen Alpheus Williams temporarily commanded the corps until Joseph Mansfield assumed command on September 14.
The III Corps and XI Corps had both suffered severe losses at Second Bull Run and were almost driven from the field in panic; they were left behind in Washington, D.C., to rest and refit. The III Corps were excellent troops who had fought hard on the Peninsula and at Second Bull Run, while the XI Corps, consisting of a large number of German-American troops, as well as its commander Maj. Gen Franz Sigel had a poor reputation and no record of success on the battlefield.
McClellan was thus able to use his influence to remove several underperforming generals, namely McDowell, Heintzelman, and Banks; the Army of the Potomac in this regard was a little behind its Confederate opponent as Lee had been able to purge his ranks of inadequate generals in the aftermath of the Seven Days Battles. The administration had wanted to remove Porter and Franklin, whom they considered politically suspect, but McClellan was able to retain them for this campaign.
Of the six corps that participated in the Maryland campaign, the II and VI were the largest and most well-rested as neither had fought since the Seven Days Battles. The II Corps received a new division of nine month troops commanded by Brig. Gen William French and the VI Corps had one new regiment; all the rest of the men in both corps had fought on the Peninsula. The I Corps was the smallest, as it had suffered heavy losses at Second Bull Run and would lose still more men at South Mountain; it is estimated that the corps had 8,000 men at Antietam out of a paper strength of 14,000. The VI Corps was also joined by Darius Couch's division, formerly part of Erasmus Keyes's IV Corps, and now being brought up from the Virginia Peninsula.
The V Corps was heavily engaged in the Seven Days Battles and at Second Bull Run, and had lost significant amounts of men; several new regiments of green troops would replace them. A new division of nine month regiments led by Brig. Gen Andrew A. Humphreys was added, but they would not arrive until after Antietam.
The IX Corps had had two divisions at Second Bull Run ; for the Maryland campaign, it was joined by a third division under Brig. Gen Samuel Sturgis and Brig. Gen Jacob Cox's "Kanawah" Division, on loan from the West Virginia area. It included several green regiments and the corps as a whole was quite inexperienced as Second Bull Run had been the only serious engagement it had fought in.
The XII Corps had not fought at Second Bull Run and its last engagement had been at Cedar Mountain a month earlier; some men from this corps were left in the Washington defenses and swapped for a number of green regiments. After Nathaniel Banks was fired on September 12, the senior division commander, Alpheus Williams, commanded the corps for a few days until Maj. Gen Joseph K. Mansfield, an old regular army officer with 40 years of service, was named to command.