In 1940, the federal government required a Detroit builder to construct a six-foot-high, half-mile-long, north-south concrete wall. The express purpose was to separate an all-white housing development he was constructing from an African-American neighborhood to its east. The builder would be approved for a Federal Housing Administration (FHA) loan guarantee he needed only if he complied with the government's demand.

Today, most African Americans in every metropolitan area remain residentially concentrated or entirely separate. That fact underlies or exacerbates many of the nation's most serious social and economic problems, from relatively low intergenerational mobility to the disproportionate prevalence of hostile encounters between police and disadvantaged black youths in neighborhoods without access to good jobs. The Detroit wall offers a striking illustration of an underappreciated truth about this shameful situation: Racial segregation in America was, to a large degree, engineered by policy makers in Washington.

Beginning in the 1930s, civil rights litigators won court victories that desegregated law and graduate schools, then colleges and, with 1954's Brown v. Board of Education ruling, elementary and secondary schools. These legal victories helped to spur a civil rights movement that, in the 1960s, forced an end to racial segregation in public transportation, in public accommodations, in employment, and in voting.