The Antietam Battlefield tour placards all now refer to the Confederates as “the enemy”.
That's Slick's political-warfare department at work. He called in Eric Foner and James McPherson to give authorial legitimacy to his own political derogation of the South, which was central to all his, and Obama's, efforts to "break the box": the Finkelstein Box.
The Box is a constellation of States from Florida to the Mountain West that the 'Rats have to break into to get at the baby. They have to demonize Southern conservatives as Them, and try to encourage Midwestern moderate conservatives to dissociate themselves from the ineffably horrid Them and vote for the nice Democrats.