That's because America is the great "melting pot" - we take people from all the other continents and throw them together over here and that's why we have so many "mutts" - it's kind of cool, actually! Everybody in the U.S. is a "something-American", since the only people native to this country are American Indians.
I guess I'd have to call myself a "European-American". I am German, Irish, Swedish, and English - mostly German though. I don't really speak any languages other than American English, although I know a lot of British words and one or two Spanish ones from my junior-high Spanish class several centuries ago.

I think it would be neat to have a one-country background - it would make researching your family tree a lot easier