No I said after WW2 with an increase in income there was a shift to suburbanization. The "single family home with the white picket fence, 2.5 kids, and a dog" was the target lifestyle.
This caused a shift in city demographics where the "haves" started moving out and being replaced with "have nots" or rental units like you see in the TV show "Friends" where landlords jam 3+ unrelated people with mediocre jobs into apartments to get more rent.
You then end up with a city suddenly needing to throw precious tax dollars at services for lower income people (like welfare) instead of using it for schools and infrastructure maintenance. As more and more money is siphoned away more and more people start moving out because they are not seeing much benefit for their tax dollars (like good schools for their kids). It then goes into an ever increasing downward spiral.