[shiroiushi]

I think it was an enormous factor. Just google for "white flight". While the rise of the automobile was a big enabler, there were other factors like the real estate industry practicing "redlining" which prevented Black people from moving into the suburbs to follow the white people who were abandoning the inner cities.

If you don't realize just how horribly racist most Americans throughout most of the 20th century, you must not be very old. I still remember how commonplace it was in the 1980s even.