<p>It’s not surprising that a person in the UK might be ignorant of ethnic and national identification in the U.S., because it’s complicated. It also varies significantly be region of the country. For example, in the South, whites are much less likely to think of themselves in terms of their European origins. In northern and midwestern areas, though, this is very different, in part because of more recent waves of immigrants. As other posters have noted, many Americans retain customs and foods from their countries of origin. In some cases, this is also connected to religion. (Interestingly, hardly anybody thinks of himself as being an English-American, though.)
Still, most of these people still think of themselves as thoroughly American, and have no particular allegiance to the country from which their ancestors came.</p>