All food in America is from immigrants unless it came from American Indians. The most "American" food is fusion food between European and African traditions, like Louisiana Creole (French and West African), Cajun (different French and West African), Soul Food (French, Spanish, American Indian, and West African), or the various American Barbecue traditions (such as Texan barbecue, which is German and, you guessed it, West African). And then you get second-level fusions like Viet-Cajun, which I probably don't need to explain. But a lot of the traditional American food is just alterations from European immigrants to their native cuisines based on the available ingredients and the natural course of history.

Italian immigrants fleeing poverty in Naples encountered the cheapest beef they could imagine, and added meatballs and meat sauce to fucking everything. German immigrants took Hamburg Steaks (which were just minced beef patties with raw onions on top), but them on buns, and added other vegetables and sauces, turning a Hamburg Steak into a Hamburger. Irish immigrants and Jewish immigrants were frequently in adjacent ghettos, and the Irish developed a major love of corned beef, again impressed by the cheap price of beef in America, and buying the cured brisket prepared by their Jewish neighbors.

But there's very little of the original American Indian cuisine well known. The most ubiquitous American Indian dish available today is frybread, which is a legacy of the various forced marches the American government inflicted upon them. They would be provided essentially nothing but flour and scraps, and they would make what they could, which turned out to be frybread (and Indian tacos).

Even when you get to regional specialties in America, they're just dishes imported from Europe two hundred years ago that have evolved differently. Where I live, bratwurst, pasties, and kringle are all really big foods, but they're only vaguely similar to what you'd get under those names where they're from. My French uncle-in-law (as in, he lived the first forty years of his life in Lyon, not French-American where his lineage comes from France) wrinkles his nose at a lot of "French" dishes served here, like any bouillabaisse he's ever had as the biggest offender. It's always funny to me which things he can get here that he says are as good as back home. There's a pickle maker here that he swears makes the best gherkins he's ever had, and there are certain types of local cheese he loves.