I always find the anti-Americanism from Britain a little hilarious when compared . After all, you were their former colonies (the original 13 states were individual colonies), and I have never heard of British anti-New Zealandism or anti-Canadianism - anti-Australianism is another matter since the Aussies regularly beat Poms in sports. A majority of American food, at least up until the Hispanic/Mexican influence over the last 15 years, is based on British diets like apple pies, roast beef. In fact, it was the British who invented the modern concept of fast food business via fish and chips shops and milk bars.
Speaking of America vs Britain, note that in Britain the collegiate University of London still has one constitutent college called the Imperial College, that people denounce "American imperialism" like Harold Pinter still receive honour titles like OBE (Order of the British Empire), some British people still treat the ex-colonies as if they were still run from London. And these same British poeple who now decry Gitmo or Abu Garib conveniently ignore what happened during the Malayan Emergency which onlyt occured half a century ago.
The British claim "you quest for world leadership, now you have to know you need to take all insults from all over the world" and they then dish out their own.
The effects of the pre-1880 immigration waves did not overly impact the overall British character of American food. The Irish had virtually no impact despite their large numbers, inasmuch as Irish cooking is very similar to British and traditional American styles. German, Dutch, and Scandinavian food are not greatly different from British models, though Germans are more liberal in their use of spices than are the British, possibly due to French, Italian, and Slavic influences. German influence is most noteworthy in beer, since their lagers and pilseners are the ancestors of most American beer. The three largest American brewers, Miller, Budweiser, and Coors, have German roots. African influence impacted cooking styles, especially in the South, in the areas of deep frying and barbecuing. Yams and okra are vegetables of African origin. The extensive use of rice in lowland Southern cuisine may also have its roots in Africa.
Another element in American cuisine is the introduction of foods native to this continent: potatoes, pecans, corn, and tomatoes, to cite several examples. Corn often substituted for other grains; grits, popular in the South, became a substitute for oatmeal, as the warmer climate of the region made oats a less viable crop than in the British Isles. Corn bread also substituted for old British staples like scones.
Between 1880 and 1920, there was a large influx of Italians, Jews, and mostly Slavic Eastern Europeans into the United States. Their immediate impact was noted in the Northeast, the Great Lakes region, and California. While their distinct cuisines were well-established through domestic and foreign suppliers, their impact outside their immediate community was minimal. Seventy years ago, a New Yorker of German, Irish, or British ancestry was likely never to have eaten spaghetti and meatballs, or bagels and lox, despite the very large Italian and Jewish communities in that city.
Baby Boomers and later generations tend not to be aware of the major impact World War II had on American society. Not only did it have a more widespread effect on human lives and the economy than any war since the Civil War 80 years earlier, it also decisively changed generations old habits. A second generation Polish-American who may have lived in a mostly Slavic mining or steel town near Pittsburgh or a Kentuckian of colonial British ancestry whose family may have farmed the same land since the late 1700s found themselves in exotic places with a wide assortment of other Americans. Add to the effects of the war the rise of a consumer oriented economy, the wide popularity of television, and an automobile centered transportation system in the postwar era, and the old ethnic and cultural isolations diminished.
The most important development in American food in the 60 years since V-J Day is the widespread diffusion of Italian, Chinese, and Mexican food on a national basis. All three cuisines are now represented in virtually every sizable town in the country. Granted, Italian food is superior in downstate New York and New Jersey and Mexican food is better in South Texas and New Mexico, but consider that 50 years ago, you would have a hard time finding dim sum or enchiladas in, say, Minnesota. Thirty years ago, just about anywhere south of Maryland and west of eastern Ohio (Detroit, Chicago, and St. Louis excepted), pizza was made with cracker thin crusts, usually with ingredients unknown to Italian Americans. Other societal trends such as single parent and two income families, the ubiquity of fast food and prepackaged meals, the geographic separation of extended families within the country, and improved selection and variety of foods at the supermarkets tended to overtake historic methods of food preparation.
However, all the trends noted in the last paragraph may be noted, to a greater or lesser degree, in all English speaking nations, as well as Western Europe. For better or worse, what is served as home, in London, Chicago, or Sydney, bears small resemblance to what their great-grandparents ate.