Okay, well, this is an outsider's opinion on this, so if some of my facts about the American school system are wrong, forgive me.
I am (obviously) not American, but from what I'm hearing here, I probably have a more diverse persepective on your history than you do. There's a funny little joke we like to say up here in Canada; Canadians know more about America than Americans know about... anything. I always thought that was a bit of an exageration... but now I'm starting to wonder.
Perhaps it's not the diversity of your own history that is the problem. Perhaps it's the lack of any other histories. In the Canadian system we learned it all (at least when I was there) African, European, Asian, Canadian and American. I can name your presidents, can you name any Prime Ministers of Canada?
Perhaps if your history classes (and pardon me for saying it your government) were a bit less focused on "Rah Rah America!" it would be easier to see the diversity in your own (and everyone else's) history without it being a huge deal.