The 1959 overthrow of Cuba's dictator, Fulgencio Batista, by the forces of Fidel Castro unleashed a wave of emigration. Most who left the island nation - which lies just 90 miles from Key West, Florida - headed for the United States. And, because Castro was a Communist who repressed Cuba's more prosperous citizens, the Cubans who arrived in the United States in the first years of the Castro regime came primarily from the upper and middle classes. Later, however, Cubans from all socioeconomic groups sought to escape their country's harsh government - often by making the perilous journey across the Straits of Florida in makeshift boats. In 1980, Castro allowed more than 125,000 citizens to leave Cuba from the port city of Mariel, adding to the already - large Cuban-American population in south Florida. Today, Cuban Americans number in the millions. They make up one of the most vibrant and prosperous immigrant communities in the United States.