Until the First World War, almost all African-Americans lived in the rural South. By 1970, almost half of the African-American population lived in cities outside the South, while many others had migrated to Southern cities. That “Great Migration” fell in two parts. From 1915 to 1930, about 1.5 million African-Americans moved out of the South. From 1940 to 1970 another 5 million people moved North or West.
The migrants found no warm welcome from the white residents of cities. Generally, white people did not want to live or work in proximity to black people. Southern cities sometimes had ordinances that forebade people of one race to live in neighborhoods where the majority population belonged to another race. However, in 1917, the Supreme Court held that such ordinances violated the 14th Amendment.
As the “Great Migration” began during the First World War, it encountered violence from northern whites. For example, in Chicago’s Washington Park between 1917 and 1921, bombings struck black-owned residences in traditionally white areas and the offices of realtors who sold houses to blacks between 1917 and 1921. A bloody race riot shocked Chicago in Summer 1919. Businessmen, and realtors in particular, saw violence as bad for business. Integration led to violence. So segregation had to be preserved.
A solution soon came to hand. The “Great Migration” coincided with an effort at Republican “Progressive” reform launched by Herbert Hoover, the Secretary of Commerce in the Harding and Coolidge administrations. In 1922, Hoover’s Commerce Department issued a model law for the states to pass called the “Standard State Zoning Enabling Act.” The model law, subsequently revised, became the common basis for urban zoning.
While the Commerce Department’s model law made no reference to racial segregation, it provided a framework within which city officials and real estate developers could use zoning and legal covenants attached to new subdivisions. Immediately after a Supreme Court decision upholding covenants in 1926, the Chicago Real Estate Board promoted the use of covenants.
What was true in Chicago’s Washington Park section was true elsewhere. Many real estate developers attached “exclusionary covenants” to each property in a sub-division. They barred sale to or occupation by African-Americans. For almost three decades, legally-enforceable residential segregation spread through much of urban America.
The National Association for the Advancement of Colored People (NAACP) mounted legal challenges to the covenants. In 1926 the Supreme Court rejected NAACP arguments and affirmed the legality of the covenants as “private action” not covered by the 14th Amendment. In 1940, the Supreme Court did reject one exclusionary covenant on technical grounds, but did not declare against covenants in general. In 1948, the Supreme Court essentially reversed the 1926 decision. The Court held that private individuals could abide by the covenants, but that they could not use the courts to enforce their own views on others.
In 1968, Congress passed the Civil Rights Act. Title VII of that act is known as the Fair Housing Act. It barred discrimination on the basis of race, creed, gender, or national origin.
 By 1970, 40 percent lived in the North, 7 percent in the West, and well over half of African-Americans living in the South lived in cities. See: Nicholas Lemann, The Promised Land: The Great Black Migration and How It Changed America (1991), and Isabel Wilkerson, The Warmth of Other Suns: The Epic Story of America’s Great Migration (2010).