What you describe mioors what happened in a lot of industrial cities, DC included.
I was very curious after see a local short about a long-time photographer (African-American) from Silver Spring/Bethesda where they profiled a lot of his work in his community. There were many, many pictures of affluent looking African-Americans from the turn-of-the-19th century.
It begs the question, “what the heck happened?” Why the “New Deal,” public housing (government sponsored ghettos)and welfare, of course — lots of social engineering.
I saw a lot of this first hand as a very young boy in Marin City, California in the early 1950s. (You should google “Marin City”)
Googling it does give a similar story to what happened in cities in the northeast.
It is a shame to see how so much changed for the worse over the decades...