The United States’ ability to desegregate metropolitan areas is hobbled by historical ignorance. Believing that segregation is de facto, resulting mostly from private prejudice and income differences, policymakers have failed to consider aggressive initiatives that are constitutionally required to remedy state-sponsored de jure segregation. First with the Public Works Administration, later with war housing built for defense-plant workers during World War II, and still later with the explicit acceptance of racial segregation by the 1949 Housing Act, the federal government created separate neighborhoods for blacks and for whites, often in cities that had not previously known such extreme racial segregation. Subsequently, whites left public housing when the Federal Housing Administration financed suburban development with requirements that builders exclude African Americans. Many other federal, state, and local government policies purposefully contributed to segregation but have never been remedied because policymakers are unfamiliar with this history and the obligations it has generated.