As world cultures have come into greater global contact, their indigenous musical styles have often merged with other styles, which produces new styles. For example, the United States bluegrass style contains elements from Anglo-Irish, Scottish, Irish, German and African instrumental and vocal traditions, which were able to fuse in the United States' multi-ethnic "melting pot" society. Some types of world music contain a mixture of non-Western indigenous styles with Western pop music elements. Genres of music are determined as much by tradition and presentation as by the actual music. Some works, like George Gershwin's "Rhapsody in Blue", are claimed by both jazz and classical music, while Gershwin's "Porgy and Bess" and Leonard Bernstein's "West Side Story" are claimed by both opera and the Broadway musical tradition. Many current music festivals for non-Western music include bands and singers from a particular musical genre, such as world music.