Take Manhattan, for example....
Where once the Dutch lived, exclusively, the English took over, the Dutch moved up north, then the English followed, and where slaves and free blacks once were buried, became yet another race and ethnics purview. The Irish took that area away from the "native born", followed by the Italians, who were then moved over by the middle Europeans and the Chinese.
Let's now move uptown some, to the East side...what was once immigrant Irish and European Jewish, suddenly became a venue for the "ELITE".
Up a bit farther ( Yorkville ), what was once mainly German and Hungarian, became YUPPIEVILLE.
And don't even get me started on the West side, because that's even MORE riddle with move up, move out, move higher, be invaded by a yet different ethnic group/s. Of course, there are the other four boroughs...take the Bronx; PLEASE!
All of these groups did MELT! Their children and grandchildren and great grandchildren and on and on and on...spoke English, assimilated, moved out of the "Little Italies, Germanies, Polands, Russias, Chinas, Hungaries, etc. and were just as much Americans, as those whose forebears came over on the Mayflower! And, by now, these groups have all intermarried, as well.
Are there places nobody in their right minds would venture into today? Yes. Is that something "new"? ABSOLUTELY NOT!
So what exactly is it, that you're trying to say, by obfuscating instead?
By the way, these Dutch were big time into slavery (in the early 18th century, the most heavily slave area in the United States was Flatbush, 45% slave), and slave trading. The Dutch who came later, and moved to the Midwest, were militantly anti slavery. Ethnic history is complex.