Populated for centuries by aboriginal peoples, the island was claimed by the Spanish Crown in 1493 following COLUMBUS' second voyage to the Americas. In 1898, after 400 years of colonial rule that saw the indigenous population nearly exterminated and African slave labor introduced, Puerto Rico was ceded to the US as a result of the Spanish-American War. Puerto Ricans were granted US citizenship in 1917. Popularly-elected governors have served since 1948. In 1952, a constitution was enacted providing for internal self government. In plebiscites held in 1967, 1993, and 1998, voters chose not to alter the existing political status.