science

I'd argue that the US definitely has and had different cultures throughout it, hell the 13 colonies all had different cultures from eachother. The only reason it seemed like there was ever a unified culture is because WW1, the Great depression/dust bowl, and WW2 caused lots of folks to move about and amalgamate culturally. Note I ain't talking about the cultural melting pot but moreso it's nutrient paste cousin where everything is homogeneous to the point of having no flavor, the type of culture that lots of suburbanites have that you can find in SoCal as easily as you can find it in Massachusetts.