I asked, "did the slums exist before the highways and freeways that divide them from the wealthy whites?" The best I've come up with is "Sort of."
Apparently, in the 50's and 60s, city officials throughout the US thought of urban freeways as "a good opportunity to get rid of the local 'niggertown.'"[1] But that attempt at clearing the local slums ended up further disrupting and distressing them, deepening the problem.
[1] Google Books: Downtown, Inc: How America Rebuilds Cities https://goo.gl/mdgYXE