June 1915

In Guinn v. United States, the Supreme Court unanimously struck down Oklahoma's grandfather clause, which exempted men whose ancestors could vote before 1866 from literacy tests — effectively protecting illiterate white voters while subjecting all Black voters to the tests. It was the NAACP's first major Supreme Court victory and the first time the Court struck down a law as a violation of the 15th Amendment since Reconstruction. Oklahoma responded by passing a new law restricting new voters that the Court later invalidated in Lane v. Wilson (1939).

In Guinn v. United States, the Supreme Court unanimously struck down Oklahoma's grandfather clause, which exempted men whose ancestors could vote before 1866 from literacy tests, effectively protecting illiterate white voters while subjecting all Black voters to the tests. It was the NAACP's first major Supreme Court victory and the first time the Court struck down a law as a violation of the 15th Amendment since Reconstruction.

The Supreme Court strikes down the "grandfather clause" used to disenfranchise Black voters.