The American Civil War might work, since enough time has passed for people to take it lightly (reenactment hobbyists, lol), but take it into this century and you might run into problems even Hetalia can't laugh away. I for one do not want to see the Rwandan Civil War discussed there, EVER. And I think Hetalia will probably go into the Vietnam War at some point, but I don't want to see it talk about the civil war aspect either. It likely won't, much like how it parodies WWII but steers clear of the Holocaust.