One of my Ethnic Studies students, before the final exam, came up with the most clever metaphor for American history I've heard in a while. American history, he said, is like a big game of immigrant whack-a-mole. The powers-that-be wield the hammer. Indians pop up? Whack! Irish? Whack! Blacks? Chinese? Whack, whack!
It was one of the most clever things I've heard a student say in a long time. For a second, I was tempted to give him an "A" just for that comment...but only for a second. If I could remember his name, I would tell ya.
Incidentally, here's a java whack-a-mole game.