When Oklahoma joined the Union in 1907, its constitution allowed all men to vote, regardless of race. In 1910 it introduced a “grandfather clause” through an amendment to the constitution. This clause provided an exemption to literacy requirements for direct lineal descendants of citizens who had been legally able to vote on or before January 1, 1866. In other words, anyone whose father or grandfather was white. The Supreme Court ruled that Oklahoma’s grandfather clause was unconstitutional in ‘Guinn’ v ‘United States’. Oklahoma legislators subsequently passed a law that required everyone except those who had voted in 1914 to register within an 11-day period or be perpetually disenfranchised (deprived of the right to vote). The Supreme Court struck down this law as well, but not until 23 years later.