It is rather interesting that the Western Art has dominated the world, while other music/arts has been only locally known in their specific region, or country. Not until Bartok has arrived, we're not only discovered the field of ethnomusicology, but there's also a crazed to embrace other musical features world wide, such as Indian music (Messieans: "Mantra,"for two pianos and live electronics, and "Stimmung," for six singers and electronics), Petatonic scales (Debussy: Estampes), Balinese orchestra (Colin McPhee: "toccata for orchestra"; also Debussy),European, especially Romanian folk tunes (Bartok: String Quartets No.3, and Romanian dances) etc.
Ethnomusiclogists such as Bartok himself, found there is a need to explore real human emotions. Reasons why we consider these transcriptions as 20th century music is due to the fact that the composer is in the 20th century era, despite the materials that he gathered was more than hundred years ago. Because he was the first to transcribed Eastern European folk tunes and infused with Western harmonies. We see it as innovative. But, what's really interesting is that we don't necessary perceived them as traditional "folk tunes" as an essential musical element. Instead we still analysis these folk tunes with Western theory symbols.
What I don't understand is: If we valued the folk tunes so highly as a part of 20th century music practice. Then, is it fair to say that what we perceived as "ancient" or "traditional" practice is a modern creation as long as there's an infusion invovled? Therefore, the raw creativity will be consider as "present" music taht represents today; in which symbolized our present society. If such "present", (20th century) music that we create today will surivived into in the next decades then, it will consider as a "high" art, or "class." In order words, the categorization of arts really does rely on time reference --- not how we perceived it as.