During the second half of the twentieth century there were three significant waves of immigration to the United States. The first period began in 1961, when a coalition of high-ranking Dominicans, with assistance from the CIA, assassinated General Rafael Trujillo, the nation's military dictator. In the wake of his death, fear of retaliation by Trujillo's allies, and political uncertainty in general, spurred migration from the island. In 1965, the United States began a military occupation of the Dominican Republic and eased travel restrictions, making it easier for Dominicans to obtain American visas.