In a comment, David reminds us today is the 145th anniversary of America’s bloodiest day. NewMexiKen has written about Antietam often:
The Deadliest Day in American History
Antietam National Battlefield (Maryland)
Thenceforward, and forever free
The best single volume on Antietam is Stephen Sears’s Landscape Turned Red: The Battle of Antietam
Sears wrote a good article on the battle in 1989: Antietam: The Terrible Price of Freedom.