>>508106733
Fair Housing Act. The decline in the Sopranos universe was actually addressed in The Many Saints of Newark I believe, showing the blacks moving in and the Italians moving out.

Read White Flight/Black Flight or at least watched the Academic Agent video about it, it tells what happened pretty well and touches on why HOAs developed in America.
https://www.youtube.com/watch?v=0-UBd_hs0Xs