The Battle of Antietam, which occurred this week (Sept. 17) in 1862, was the bloodiest one-day battle of the Civil War and remains the bloodiest one-day battle in American history. After a string of victories in Virginia, a Confederate army under Robert E. Lee was making its first foray into Union territory, where it met a Union army under General George McClellan at Antietam Creek, Maryland. McClellan was greatly aided by advance notice of Lee’s battle plans—a careless Confederate officer had lost them and a Union soldier had found them—but even so, the battle was a tactical draw.
Strategically, however, it was a Union victory because Lee was forced to retreat back to Virginia. More important, Antietam also convinced Great Britain not to recognize or support the Confederacy, which undoubtedly changed the outcome of the Civil War.
Before Antietam, British recognition of the Confederacy was a real possibility. For one thing, Britain’s critically important textile industry was hugely dependent on cotton and 70 percent of Britain’s cotton imports came from the South.
For another, by the 1860s Britain was becoming increasingly nervous about the growing power and influence of the United States, so the prospect of recognizing the Confederacy as a separate nation, thereby splitting America into two smaller and weaker countries, had real appeal.
But there were drawbacks. In 1862 Britain also greatly depended on imports of foodstuffs from America — wheat, corn and barley — which mostly came from northern states. Also, being an empire, Britain made it a point not to support rebellions (no doubt recalling the one against them in 1776). Complicating matters, the Lincoln administration suggested that war might result against Britain if it recognized the Confederacy, a war the British worried could spread to Canada, a British possession many Americans coveted.
And finally, Britain subscribed to the principle that you recognize a government only when it has shown it can maintain its independence, which the Confederacy had not yet done.
It was this last principle that made Antietam so important. Had the Confederacy won that battle many in the British government were prepared to both recognize and support the Confederacy, which would have tipped the war in its favor.
In addition, had Antietam been a Confederate victory, Lincoln might not have issued his Emancipation Proclamation — he was waiting for a Union victory before announcing it. That proclamation changed the North’s war aims from merely preserving the Union to ending slavery as well, which ended all chance of the slave-holding South gaining British support because Britain had a large and very vocal abolitionist movement.
So in addition to being the bloodiest one-day battle in American history, Antietam was almost certainly the most politically consequential.