title: Calypso music
context: The first major stars of calypso started crossing over to new audiences worldwide in the late 1930s. Attila the Hun, Roaring Lion and Lord Invader were first, followed by Lord Kitchener, one of the longest-lasting calypso stars in history—he continued to release hit records until his death in 2000.  1944's "Rum and Coca-Cola" by the Andrews Sisters, a cover version of a Lord Invader song, became an American hit despite the song being a very critical commentary on the explosion of prostitution, inflation and other negative influences accompanying the American military bases in Trinidad at the time.[6] Perhaps the most straightforward way to describe the focus of calypso is that it articulated itself as a form of protest against the authoritarian colonial culture which existed at the time.
question: When did calypso music become popular in the U.S.?
answers: late 1930s