sentences:  After slavery was abolished in the United States in 1865, American planters imported temporary workers, called "swallow migrants", to harvest crops on an annual basis.These workers, many of them Jamaicans, returned to their countries after harvest.Between 1881 and the beginning of World War I, the United States recruited over 250,000 workers from the Caribbean, 90,000 of whom were Jamaicans, to work on the Panama Canal.