See my earlier comment. My parents lived in those "ethnic enclaves" (Dad in Newark, mom in Jersey City) you speak of. What really happened is that after WWII, many of the upwardly mobile moved to the suburbs, which depressed property values considerably, making it affordable for blacks and new immigrants to move in.
(Don't take anything Michael Jones says too seriously).
What really happened is that after WWII, many of the upwardly mobile moved to the suburbs, which depressed property values considerably, making it affordable for blacks and new immigrants to move in. I'd include VA loans in that equation, and developers in outlying areas who marketed developments to vets, and others who needed the financing they could arrange.