1898: Spain cedes Puerto Rico to the United States at the close of the Spanish-American War through the Treaty of Paris.

1902: The United States declares Puerto Rico a territory.

1917: The Jones Act gives Puerto Ricans U.S. citizenship and a locally elected legislature; executive authority remains in the hands of a governor appointed by the U.S. president.

1947: Congress permits Puerto Ricans to elect their governor, effective in 1948.

1952: Congress ratifies a local constitution for Puerto Rico, subordinate to and compatible with the U.S. Constitution; the territory is denominated a commonwealth.

1967: In the first plebiscite on the island’s status, Puerto Ricans endorse commonwealth over statehood, 60 percent to 39 percent. Independence garners 1 percent of the vote.

1993: In a second plebiscite, the commonwealth polls 48.6 percent to statehood’s 46.3 percent, with independence at 4.4 percent.

1998: A third plebiscite, offering four options based on legislation approved earlier that year by the U.S. House of Representatives, generates 46.5 percent backing for statehood; nearly all of the remaining votes (50.2 percent) are cast for “none of the above” in a protest led by commonwealth advocates. 

Sources: Time Almanac 1999 and the Office of the Governor of Puerto Rico.