In Guinn v. United States, the U.S. Supreme Court finds unconstitutional Jim Crow laws, which helped enforce segregation in Southern states. Specifically, the Court declares unconstitutional the “grandfather clause” in the Oklahoma Constitution, which allowed illiterate men to vote if they could prove that their grandfathers had the right. As a result, illiterate white men could vote but not illiterate blacks, since as a general rule their grandfathers had been slaves.
Such regulations, which were intended to disenfranchise former slaves and other people of color, continued to persist as a method of circumventing the specific wording of the 15th Amendment well into the 20th century.