Houston also directed the NAACP's campaign to end restrictive housing covenants. In the early 20th century, the organization had won a United States Supreme Court case, "Buchanan v. Warley" (1917), which prohibited state and local jurisdictions from establishing restrictive housing. Real estate developers and agents developed restrictive covenants and deeds. The Court ruled in "Corrigan v. Buckley" (1926) that such restrictions were the acts of individuals and beyond the reach of the constitutional protections. As the NAACP continued with its campaign in the 1940s, Houston drew from contemporary sociological and other studies to demonstrate that such covenants and resulting segregation produced conditions of overcrowding, poor health, and increased crime that adversely affected African-American communities. Following Corrigan, Houston contributed to what was a 22-year campaign, in concert with lawyers he had trained, in order to overturn the constitutionality of restrictive covenants. This was achieved in the US Supreme Court ruling in "Shelley v. Kraemer" (1948). The court ruled that "judicial enforcement of private right constitutes state action for the purpose of the fourteenth amendment." Houston's use of sociological materials in these cases lay the groundwork for the approach and ruling in "Brown v. Board of Education" (1954).