In northern cities, the black population is quite recent, and urban renewal programs predate much of the Great Migration. The Great Migration was itself weaponized by WASP elites against the European and very often Catholic ethnic neighborhoods in northern cities (who were out-procreating the WASPs given their stance on contraception, for example, which differed from the Protestants who had began to accept its use in the 1930s).

To disguise the project, terms like "white flight" were invented in order to frame the disintegration of these European neighborhoods as a racist reaction. This worked especially well during the Civil Rights movement, because it played on black/white categories in the forefront of everybody's minds. But were these European ethnic groups "white"? We already know that the Irish and the Italians weren't considered "white" until recently.

Perhaps you've seen videos of "white people" in Chicago throwing rocks at black marches led by MLK into these ethnic neighborhoods? These were people, like Lithuanians, who were defending the integrity of their neighborhoods from an invasion. That the marching masses entering their neighborhoods were black is completely irrelevant: any mass migration of another cultural group into a host population harms and destroys the integrity of the host population. And that was the point. White flight destroyed the ethnic neighborhood through mass migration and the subsequent dispersal of them across the newly created suburbs. This process hastened their assimilation into an amorphous mass shaped by the mass media. These assimilated groups formed a buffer between WASP neighborhoods and the neighborhoods of the new black arrivals from the South. The construction of highways played a similar role by erecting psychological or physical barriers between these neighborhoods. They were also used as excuses to demolish "undesirable" neighborhoods.