In the late 1800s, Harlem was an all white community of middle and upper middle class whites, or varying ethnicities.
It wasn't until the beginnings of the 20th century that blacks moved there and it wasn't until WW II, that Puerto Ricans moved into a part of it.
Harlem has been in the midst of a white influx and a massive gentrification for about a decade or so, now.
Yes, N.Y.C. has ALWAYS been in the midst of some kind of strum&drang, with once VERY fashionable areas turning into slums and slums turning into posh places. It's the natural history of the city!
But did they have to kill off the egg creams?
My wife's father grew up in Harlem, when it was upper middle class and largely Jewish. Of course that was before and during the First World War, before the block busters arrived.