Swedish popular music, or shortly Swedish pop music, refers to music that has swept the Swedish mainstream at any given point in recent times. After World War II, Swedish pop music was heavily influenced by American jazz, and then by rock-and-roll from the U.S. and the U.K. in the 1950s and 1960s, before developing into dansband music. Since the 1970s, Swedish pop music has come to international prominence with bands singing in English, ranking high on the British, New Zealand, American, and Australian charts and making Sweden one of the world's top exporter of popular music by gross domestic product. With the influx of American G.I.s into Europe in the 1940s, styles of American music seeded themselves into Swedish culture. Many Swedish dansorkestrar ("dance orchestras") played jitterbug, foxtrot, and swing music and other jazz-derived tunes for people to dance to. In the 1950s early rock and roll, as well as country music and German schlager also infused the market, influencing Swedish musicians to build upon these styles, gradually moving them away from jazz, which was turning more toward the avant garde. The jazz orchestra dancing in Scandinavia was interrupted by the counterculture of the 1960s, whose influences of left-wing politics and LSD were altering the shape of popular music around the world. In 1967 the first psychedelic and progressive rock groups emerged in Stockholm's Filips club, including Hansson & Karlsson, the Baby Grandmothers, and Mecki Mark Men. These groups were very popular in the Sweden of the late 60s, with television appearances, sold-out concerts, and tours around Europe. Mecki Mark Men even spent three months in the U.S. where they played big rock music festivals with Sly and the Family Stone, Jethro Tull, Pentangle, Mountain, Grand Funk Railroad, Paul Butterfield, and The Byrds. Aside from this music that blended rock, jazz, and folk music with improvisation and experimentation, Swedish progressive rock, or "progg" as it became known, was also fiercely political.