Antietam

A key turning point in the American Civil War, the Battle of Antietam - alternatively known as the Battle of Sharpsburg - was a massive, pitched battle between the Union and Confederate armies. This bloody battle that pitted the North against the South resulted in 23,000 men dead, countless injured, and an opening for an embattled President to announce the emancipation of enslaved people. Let's dig into this significant conflict!

Battle of Antietam

In September 1862, Confederate General Robert E. Lee advanced his Army of Northern Virginia into Maryland. He intended to attack the north of Washington, D.C., with a force of over 30,000 men to pull Union forces away from the northern capital and defeat them. General George McClellan of the Union's Army of the Potomac was ordered to pursue Lee. His own force consisted of around 80,000 men. After an initial skirmish near Boonsboro, Maryland, Lee's forces fell back towards the nearby town of Sharpsburg to prepare themselves for a larger fight.

Fig. 1 - Maryland, Antietam, President Lincoln on the Battlefield

Before the two forces engaged, on 13 September 1862, Union forces discovered hidden operational documents belonging to General Lee that gave McClellan insight into Lee's battle plans. Lee planned to place his troops into a false front line on 15 September as a bluff to give more time for the rest of his armies to reposition and organise themselves. McClellan - fearing he may be outnumbered - hesitated for two days to assess the situation. Then, on 16 September, he ordered parts of his army to advance across Antietam Creek.

He intended to attack the northern and southern ends of the Confederate line and then follow up with a last attack in the centre. His attacks began early in the morning on 17 September.

Antietam Timeline

Although the Battle of Antietam is seen as just one day, it is important to understand its timeline as it is known as the bloodiest day of the American Civil War.

Battle of Antietam location

The first of the Union's major attacks occurred on the northern end of the line, in which the 1^st Corps of the Army of the Potomac, under the command of General Joseph Hooker, assaulted positions held by Confederate General "Stonewall" Jackson. His objective was to capture a high-ground plateau on which sat a building called Dunker Church, located between the western and eastern woods around Miller's Cornfield.

Fighting for Miller's Cornfield and Dunker Church

From the high ground around the Church, a strong barrage of Confederate artillery hit the advancing Union infantry as they engaged with the Confederate infantry opposite them in the Cornfield. Hooker brought his own artillery to bear, and the infantry engaged in intense hand-to-hand combat, with the Union forces slowly making progress toward the Church.

The fighting took a turn as Confederate infantry under the command of General John B. Hood made an aggressive counterattack through the Cornfield, pushing Hooker's army back, though at a significant cost. Hooker called for reinforcements, which arrived in the form of Major General Joseph Mansfield's 12^th Corps. The 12^th Corps advanced on the field in a tight formation which caused them to take heavy losses under the barrage of Confederate artillery, including Mansfield himself, who took a fatal wound. Despite that, the 12^th Corps succeeded in capturing Dunker Church.

Fig. 3 - Battle of Antietam Map Morning Phase

As the combined 1^st and 12^th Corps began to take up positions near the Church, General Hooker suffered a wound and left the battlefield. Without a commander, the Union forces stalled until the arrival of General Edwin Sumner and his 2^nd Corps. Sumner advanced his divisions forward rapidly, and they became separated from each other. One division, under the command of John Sedgwick, attacked into the woods west of Dunker Church, where they were quickly overrun by a Confederate counterattack. Sedgwick was shot three times during the action and lost around half of his men before pulling back.

Though the Confederate's northern left flank under Stonewall Jackson had suffered, it still held, prompting the Union to focus their next attacks on other parts of the line.

Burnside's Bridge

On the southern part of the line, Union General Ambrose Burnside was given the responsibility to attack the Confederate southern flank to pull forces away from Hooker's attacks in the north. However, McClellan had instructed him to hold his attack until he had received his order, which did not arrive until later in the morning, around 10 AM.

Burnside chose to split a division off to make a crossing of Antietam Creek further to the south, while his main force attempted a crossing at a small stone bridge - one which was defended by Confederate infantry and cannons. His forces made repeated assaults on the bridge but were repelled several times by heavy Confederate fire until around 1 PM, when a third charge succeeded in taking the bridge. Around the same time, Burnside's other division had made their crossing further south and threatened to flank the Confederate defenders, who chose to fall back.

Fig. 5 - Battle of Antietam Map Afternoon Phase

Safely across, Burnside intended to advance along Harper's Ferry road south of Sharpsburg to cut off Lee's only path of retreat, but he was delayed by several hours moving his entire force across the bridge and reorganising them. Though his attack on the southern approach to Sharpsburg was initially successful and threatened to break the Confederate lines, the arrival of a new Confederate division under Ambrose P. Hill turned the tide and stopped the Union's assault.

• By the end of the day, both sides had suffered significant losses, and the fighting had stalled.
• Confederate lines were under threat in several places.
• McClellan hesitated to launch further attacks.
• This gave the Confederates time to organise a retreat.
• General Robert E. Lee, having lost around a third of his men, decided to pull back the Confederate Army of Northern Virginia back to Virginia and abandon his campaign.

Battle of Antietam casualties

17 September 1862 was the single bloodiest day in US History, with over 22,000 casualties on both sides combined. Though the high death toll of the battle made exact numbers difficult to determine, the following is sourced from the Official Records of the War of Rebellion and the Antietam Battlefield Board.

Battle of Antietam Significance

Though the Union did not achieve a decisive tactical victory at Antietam, they did win a strategic one. The Confederacy could not sustain the heavy losses suffered at Antietam, and General Lee was forced to abandon his invasion of the north and could no longer threaten Washington, D.C. from the northwest.

The Confederate States of America had also hoped that a major victory by Lee against the north might earn them international recognition and support, particularly from the United Kingdom, but this was unsuccessful.

Though McClellan had, in effect, won the day, he did not decisively collapse the Confederate lines and failed to capitalise on the Confederate retreat, leading President Abraham Lincoln to believe that a crucial opportunity to destroy the Confederate Army of Northern Virginia had been missed. Frustrated by McClellan's cautiousness at Antietam, Lincoln dismissed him from command in October 1862.

Nevertheless, Lincoln saw the victory as an opportunity to announce his Emancipation Proclamation at the start of 1863, which re-characterised the American Civil War as one that would be fought for the explicit abolition of slavery and also opened the door for African Americans to fight in the Union army during the rest of the Civil War.