The Confederate troops used to hide secret messages in cigars. One day when the confederates set up camp they dropped the cigars.
The Union set up camp in the exact same place and found the cigars, opened them up and found a surprise attack on them.
The Union beat the confederate to the spot of attack and surprise attack them.
The battle took place in Maryland near the town of Sharpsburg and Antietam Creek. This was the first battle in the Union States.
The Battle of Antietam was one of the bloodiest battles on the United States of America ever!
Although the battle was tactically inconclusive, the Confederate troops had withdrawn first from the fight, making it, a Union Victory. If the Union never found the cigars the result might have been different