there was someone once who said in a few generations, like 3 or 4 the people in America will be true "mutts" with to much various lineage to trace to 1 country of origin. as it is right now, many of us have direct parents or direct grandparents who emmigrated, so they is sort of an nationality in many of us.
myself, my grandparents emmigrated from Sweden, and my mother was 100% Swedish in heritage, even though she was born in Michigan.
a friend from highschool's grandparents were from Germany, and they sopke german in the home, i'd say he was "German" in a way.