At dinner I realized almost every sushi or hibachi restaurant I've been to had the exact same miso soup bowls, spoons, and little soy sauce bowls. There seem to be a lot of cuisines with a standard Americanized menu and decor (listed with the "standardized" name): Chinese, Indian, Greek, Italian, Mediterranean, Mexican, Thai, to some extent Korean...
Presumably the standardization happened in major immigration centers before spreading, but people immigrate from different areas of a country/region to different areas of the US. And that's ignoring that immigration often spans generations. So why are there not differences between say, the east coast, west coast, and midwest? I'm thinking about things like the sushi menu and bowls, hibachi chef's all having the same routine, Indian buffets, Chinese restaurants with essentially the same menu in the same font, Greek restaurants with the same paper cups, the combo options at Mexican restaurants with the same rice and beans and plates, etc.
This may be a really broad question, so if someone knows how or when this happened for one cuisine, that would be really interesting. The fact that I thought of more examples while writing this makes me even more curious.
For Chinese food, there was a concerted effort to help families set up restaurants around the US by certain Chinese business groups (like a chamber of commerce). They provided the recipes, funding, location, and so on to get them going. I have no idea what the families gave them in return.
This helped spread Chinese food around the US primarily after WW2 (and not with the railroads as many assume), and created that mostly homogenized food style we're so used to now.
There's an amazing documentary on the subject called Searching for General Tso, which goes into detail that was based on the book "The Fortune Cookie Chronicles." I highly recommend both.
Even then, though, "Chinese" food as a concept was recognized pre-WW2 even in some of the most rural Midwestern towns (even if the actual style, including the US version, was mostly unknown) with people making "chop suey" that was called Chinese, but was limited to local ingredients and had no bearing to actual Chinese food (like noodles with some kind of basic sauce).
I took a Masters class on Anthropology of Food, which covered some of that background.
As for the other styles, it really depends on the group. Hispanic or Mexican (or Tex Mex) spread along highways and railroads, but there were also many Hispanic populations around the US already.
Italian became super popular after WW1, and was pushed hard by the development of super markets, which could carry easy "Italian" ingredients with low spoilage- canned sauces, dry noodles, Chef Boyardee, etc. Pizza came on the scene later after WW2 with Pizza Hut starting (of all places) in Wichita, Kansas.
It should also be noted that many of these younger(?) ethnic food places didn't just spread "naturally," but became fads, which then spread inward from there. They were commodified either by local people moving around the US OR they became franchises and were pushed by corporate/regional companies.
I can’t speak for Indian, Mexican, or Italian food, but the Chinese Exclusion Act featured merchant visa loopholes for certain qualified businesses. This allowed Chinese Americans living in the states to legally bring workers (family & friends) from China to America to work for them. One of those qualified businesses was restaurants, so now we have over 40,000 Chinese restaurants in America.
A federal court added restaurants to the list of qualified businesses in 1915 so it was the decade and a half after that where Chinese restaurants started to gain popularity.