Urban Americans are the most distrustful of strangers though. Also, (white) Americans moved to suburbs because of a combination of cheap availability of gasoline and racism ("white flight").
http://en.wikipedia.org/wiki/Auto-segregation Humans tend to naturally segregate themselves by group when faced by diversity so they can preserve their language and beliefs.
Also, suburban sprawl has happened everywhere from Africa, China, Australia, Brazil, Mexico. Even black folk don't want to live in the city. http://en.wikipedia.org/wiki/Black_flight
Even India, Australia, China, and other countries experience suburban sprawl. Oh did they move away from black folks too? Humans, like many other animals, like having territory, land, peace, and quiet. So people work in the city but live tucked away in the county. And that the fact that in St. Louis, we have Belfontaine (the black county which has nicer areas than many of the white counties) just proves that everyone likes living in peace & quiet.
I suppose another factor is that Americans don't really do cities right, but this is largely an effect of the other two factors, plus the awkward way the American political system gives disproportionate influence to people living in less density.
Yes, there are other countries with suburbs. In some of them, the suburbs are more dense and walkable than most American cities, which much better access to public transportation. In others, suburbs are the poorer and less desirable places to live. In fact, this is starting to happen in some places in the United States! It's not just the American 1950's pattern over and over again.