James McPherson, Civil War historian, and Edwin Bearss, former National Park Service chief historian, each talked about the Battle of Antietam. After the presentations the authors together took questions from members of the audience. 
This was a key part of a program at a National Park Service program to commemorate the 150th anniversary of the Battle of Antietam. The battle on September 17, 1862, was the bloodiest day of fighting in American history. President Lincoln took advantage of the Union strategic victory to issue the preliminary Emancipation Proclamation a few days later.