Folk music was used by many composers in the Romantic period. Gustav Mahler used folk song in a lot of his music. In the early twentieth century some composers travelled around collecting folk music which was being played or sung by people in the country. They often used some of these ideas in their music. Bartok did this in Hungary as well as in Bulgaria and in the United States, and people such as Cecil Sharp and the composer Ralph Vaughan Williams collected folk music in England. In the United States the influence of jazz on classical music is all part of the story of folk music.