Melting pot or salad
I realize it's not PC to refer to America as a melting pot anymore, since the prevailing political thought is "God forbid that people should assimilate." Nevertheless, America is more of a melting pot than European countries, and recent events in France, and England, and Denmark, etc., have made it clear that we should be grateful that our immigrants are still, for the most part, melting in. Ron has put his thinking hat on and come up with a bunch of very good reasons why it's not just good luck that has us assimilating immigrants so much better than the Europeans do. Check it out.
