The patterns of black/white segregation in the "rust belt"--formerly heavily industrialized cities of the Northeast and Midwest, are the products of common historical influences. The collapse of the Southern share-cropping system in the 1930s, combined with an industrial boom in Northern cities from the 1940s on, due to wartime manufacturing, sent millions of blacks North, seeking and finding, better prospects. However, after the war these cities declined economically, as they lost their industrial base and firms moved to the suburbs. Whites were enabled by various Federal and local policies to escape the declining cities to the prosperous and growing suburbs. But the same policies did not help blacks. Whites also used class-based zoning and private housing discrimination to keep blacks out of suburban neightborhoods. Observe the high correlation of segregated areas with income in nearly all cases.

To learn more, see Douglas Massey and Nancy Denton, American Apartheid (Harvard University Press, 1993).