What really happened at the Battle of Antietam? Why is the Battle of Antietam called 'The Bloodiest Day' of the Civil War?

It all started Wednesday, September 3, 1862, four days after General Robert E. Lee's Confederate victory at the second Battle of Bull Run. Lee dispatched a letter to southern president Jefferson Davis. In this letter Lee announced his intention to carry the war onto enemy soil for the first time in the Eastern Theater. Lee hoped that a great confederate victory would encourage England and France to help the south win the war and he hoped that …

…and here we lie." Bibliography Antietam Battle Information. [Online] Available http://www.nps.gov/anti/battle.htm, January 20, 2001. Bailey, Ronald H. The Bloodiest Day: The Battle of Antietam. Virginia: Time-Life Books, 1984. "Battle of Antietam." American Heritage Illustrated History of the United States: The Civil War. 1989 ed. The Battle of Antietam (Sharpsburg). [Online] Available http://www.civilwarhome.com/ Antietam.htm, February 10, 2003. Dupuy, Trevor Nevitt. The Military History of Civil War Land Battles. New York: Franklin Watts, 1960.