…was the section near the end that explored the divergent fortunes of black internal migrants and the new European immigrants in northern cities, with Chicago being a main example.

The basic point is that the first generation black migrants were wealthier and better educated than the European immigrants, with both populations facing significant housing/neighborhood segregation. But Poles and Italians, etc. were able to quickly blend into the broader population because they weren’t visibly different, while anti-black racism and prejudice was more enduring, and over a generation or two left their descendants significantly behind immigrant families, and still highly segregated.