In the 15th century, Portuguese navigators discovered these two volcanic islands off the coast of West Africa in the Gulf of Guinea. São Tomé is the larger island with about 90 percent of the population. Africa's smallest nation gained independence in 1975. In 1991 the formerly Marxist government made a complete transition to democracy. The new leaders have moved to liberalize the economy and reduce dependence on plantation crops. New offshore oil discoveries could translate into substantial oil revenue in the near future.