Wikimedia
Wikipedia: Battle of Antietam
This Wikipedia article on the bloodiest battle in American history gives background information on the battle, the battle itself, and the aftermath.
Curated OER
National Park Service: Antietam National Battlefield
The National Park Service offers a wealth of information on Antietam, the battle, casualties, flags, and weapons. A very worthwhile site.
Other
Antietam on the Web
A comprehensive resource from Antietam on the Web of the Battle of Antietam, including historical documents, battle maps and much more.
American Battlefield Trust
American Battlefield Trust: Civil War: The Battle of Antietam
Watch this animated Civil War simulation depicting the The Battle of Antietam of 1862.
Civil War Home
Home of the American Civil War: Battle of Antietam
An overview of the Battle of Antietam along with accounts of the battle written by those who fought. Information is from several sources.
Curated OER
National Park Service: Cwsac: Civil War Battle Summaries: Battle of Antietam
This site, which is provided for by the National Park Service, gives a brief overview of the events at the Civil War Battle of Antietam.
Library of Congress
Loc: America's Story: The Battle of Antietam
What was the bloodiest battle in all American history? The Battle of Antietam , during the Civil War, wins this dubious honor. The Library of Congress has more information about this famous battle along with some actual photographs.