On September 17, 1862, a significant battle took place at Antietam Creek near Sharpsburg, Maryland, where the Union Army, led by General McClellan, fought against the Confederate Army, led by General Lee. This battle is known as the bloodiest day in American history, with over 25,000 casualties, dead or wounded. Despite the intense fighting, neither side was able to make significant gains by nightfall. Lee, who suffered a loss of up to one-third of his army, retreated to Virginia.
However, McClellan, known for his cautious tactics, did not pursue the weakened Confederate army, missing a chance to end the war sooner. As a result of his failure to act, McClellan was fired by President Lincoln in November of the same year.