Most historians call it a Pyrrhic Union victory because it prevented the south from advancing any further until the following year.
“Most historians call it a Pyrrhic Union victory because it prevented the south from advancing any further until the following year.”
Yes, as a strategic battle it would fit the definition of a Pyrrhic victory, but as a tactical battle it was a draw. It was a very pivotal fight in the War, and how it ended meant that the War would go on. The next such pivotal battle was Gettysburg, almost a year later, and THAT battle arguably cost the Confederacy the war.
But Antietam was interesting, because McClellan (who had discovered Lee’s battle plan) resorted to his usual timid self and blew it. Lincoln replaced him soon after.