of the residents of a neighborhood were of a certain race, no one from a different race was allowed to move in. That ordinance was struck down in a court challenge, by the NAACP, after which racial covenants were used to prevent the sale of houses in certain neighborhoods to "persons not of Caucasian race". Again, St. Louisans offered a lawsuit in challenge, and such covenants were ruled unconstitutional by the U.S. Supreme Court in 1948 in Shelley v. Kraemer. In 1926, Douglass University, a historically black university was founded by B. F. Bowles in St. Louis, and at the time no other college in St. Louis County admitted black students. In the first half of the 20th century, St. Louis was a destination in the Great Migration of African Americans from the rural South seeking better opportunities. During World War II, the NAACP campaigned to integrate war factories. In 1964, civil rights activists protested at the construction of the Gateway Arch to publicize their effort to gain entry for African Americans into the skilled trade unions, where they were underrepresented. The Department of Justice filed the first suit against the unions under the Civil Rights Act of 1964. Between 1900 and 1929, St. Louis, had about 220 automakers, close to 10 percent of all American carmakers, about half of which built cars exclusively in St. Louis. Notable names include Dorris, Gardner and Moon. In the first part of the century, St. Louis had some of the worst air pollution in the United States. In April 1940, the city banned the use of soft coal mined in nearby states. The city hired inspectors to ensure that only anthracite was burned. By 1946, the city had reduced air pollution by about 75%. De jure educational segregation continued into the 1950s, and de facto segregation continued into the 1970s, leading to a court challenge and interdistrict desegregation agreement. Students have been bused mostly from the city to county school districts to have opportunities for integrated classes, although the city has created magnet schools to attract students. St. Louis, like many Midwestern cities, expanded in the early 20th century due to industrialization, which provided jobs to new generations of immigrants and migrants from the South. It reached its peak population of 856,796 at the 1950 census. Suburbanization from the 1950s through the 1990s dramatically reduced the city's population, as did restructuring of industry