I think the intensity matters: my Irish ancestors weren’t considered white when they got here but there wasn’t a mass exodus from cities rather than sharing infrastructure, and they were allowed into whiteness over time (especially when large numbers of cops were needed to police black populations). The ones who served in the military weren’t restricted to certain units and duties, etc. When white people moved to the suburbs, the neighborhoods which were razed to make highways had a very uneven distribution.

That’s definitely not perfect (and it’s like, say, Chinatowns weren’t raided or sacked) but that option of coexistence wasn’t on offer in much of the country.

> all segregated into their own neighborhoods.

Check out Shellings model of segregation [0]. Global seggregation doesn't necessarily mean that local decisions have strong preference for their race.

e.g. for two types it's enough to have preference "I want at least 33% of my neighbours to be same type as me" to reach segregated global result.

[0] https://en.wikipedia.org/wiki/Schelling%27s_model_of_segrega...