"Europeans from Spain, Portugal, France and England who colonized South America and the Caribbean all imported slaves from Africa to take over the hard labor of the local inhabitants. The Rumba combined African and Caribbean rhythms in a dance that in its original form was extremely erotic and uninhibited. The lady would perform sinuous movements of the hip, chest, and shoulders, while the man did his best to respond. Since not all Cubans possessed this uninhibited quality, a refined version of the rumba named the son emerged. The son was slower and more sentimental, with movements that were mere flirtation as opposed to the promise of the real thing. The son was the actual dance exported.
The name "Rumba" now includes many types of Latin American dances, including the son. The Rumba reached the United States in the late 1920's. In 1946, the British originally standardized the Rumba. They taught it using the United States technique (with couples dancing in a square or "rumba box" rather than moving around the whole floor)." Article source: www.ctkr.com.