The bloodiest day in American history took place on the 75th anniversary of the signing of the Constitution. On September 17, 1862, Robert E. Lee’s Confederate Army of Northern Virginia fought George McClellan’s Union Army of the Potomac outside Sharpsburg along Antietam Creek. That day, nearly 25,000 would become casualties, and Lee’s army would barely survive fighting the much-bigger Northern army. Although the battle was tactically a draw, it resulted in forcing Lee’s army out of Maryland and back into Virginia, making it a strategic victory for the North and an opportune time for President Abraham Lincoln to issue the Emancipation Proclamation, freeing all slaves in the rebellious states. 

When discussing the Civil War in Maryland, most of the focus is understandably on Antietam, but it’s important not to overlook the battle that ultimately brought the Union and Confederate to Antietam Creek in the first place. The Battle of South Mountain was an opening salvo of sorts before Antietam, fought on September 14, 1862, among several gaps. 

Despite being significantly outnumbered, Lee's army had the advantage of fighting defensively on higher terrain. At Crampton's Gap, Union General William Franklin’s nearly 13,000-strong VI Corps crashed down on about 2,000 Confederates led by Howell Cobb who were part of Lafayette McLaws’ division. McClellan had ordered Franklin’s corps to set out for Crampton’s Gap on the morning of September 14, wasting nearly 11 hours in the process, and Franklin delayed his assault for three more hours while arranging his lines for what turned out to be a short fight. 

The fighting that occurred on that long Sunday was fierce and constant. Artillery, musket, bayonet, and fists were all employed as weapons, resulting in a tremendous number of casualties. By barely holding onto some of the passes, Lee was able to retreat to Sharpsburg, where he hoped to gather together his scattered forces. As it turned out, the last of the Confederates, A.P. Hill’s Light Division, would only arrive around Sharpsburg during the afternoon on September 17, while the Battle of Antietam was at its peak and Lee’s army was in danger of being surrounded and captured in its entirety. 

Thus, these men, many of whom are lost to history, engaged in a battle that led directly to the bloodiest single day in US military history a few days later along Antietam Creek, and that battle would eventually compel President Lincoln to issue the Emancipation Proclamation. The Battle of South Mountain, therefore, proved to be the catalyst for events that forever altered the course of the Civil War and the nation.

The Battle of South Mountain: The History of the Civil War Battle That Led the Union and Confederate Armies to Antietam looks at the events that led up to and brought on the Battle of South Mountain. You will learn about South Mountain like never before.