Ballroom tango is a ballroom dance that branched away from its original Argentine roots by allowing European, American, Hollywood, and competitive influences into the style and execution of the dance.
The present day ballroom tango is divided into two disciplines: American Style and International Style. Both styles may be found in social and competitive dances, but the International version is more globally accepted as a competitive style. Both styles share a closed dance position, but the American style allows its practitioners to separate from closed position to execute open moves, like underarm turns, alternate hand holds, dancing apart, and side-by-side choreography.
American style tango
American style tango’s evolutionary path is derived from Argentina to the United States, when it was popularized by silent film star Rudolph Valentino in 1921, who demonstrated a highly stylized form of Argentine tango in The Four Horsemen of the Apocalypse. As a result, the Hollywood style steps mixed in with other social dance steps of the times began this branch away from the Argentine style. Meanwhile, the tango was also making its own inroads into Europe.
Following the English standardization of their version of tango, Arthur Murray, a ballroom dance instructor in the U.S., tried his own hand at standardizing the ballroom dances for instruction in his chain of social dance schools. This looser social style was referred to as American style by the English.
source: wikipedia
