Reddit reviews Balkan Popular Culture and the Ottoman Ecumene: Music, Image, and Regional Political Discourse (Europea: Ethnomusicologies and Modernities)

Theory:

• Kalin Kirliov - Harmony in Bulgarian Music (PhD Diss)
  
  
• Borislav Petrov - Bulgarian Rhythms: Past, Present and Future
  
  Ethnomusicology:
  
  
• Carol Silverman - Romani Routes: Cultural Politics and Balkan Music in Diaspora
  
  
• Balkan Popular Culture and the Ottoman Ecumene: Music, Image, and Regional Political Discourse, ed. Donna Buchanan
  
  
• And there's a ton more. Read the bibliographies.
  
  You'll notice that Bulgaria is over-represented here. Unfortunately, this is as far as my knowledge of the literature extends. However, one of the ideas you'll encounter in all of the sources I have listed is that the idea of the nation-state is not congruent with the musical realities of "national style" unless the nation-state invents a national style (which did happen). The Balkans have always been contested and borders have always been fluid. "Turkish" music was officially banned in socialist Bulgaria, but the wedding bands all basically played Turkish music amalgamated with whatever else people wanted to hear. And they did the same thing in Macedonia, Greece, etc.. There are some elements that come out of geographically specific practices (which nation-states attempt to preserve and amplify in folklore), but in the 20th century you see a lot of styles and a lot of mixture.