As part of my Bulgarian holiday I purchased a real physical copy of "The Balkans" by Mark Mazower. I had to buy a real book, because you are still not allowed to read a kindle when you land or take off in a plane -- but I believe that rule is slowly changing.
The book was a good short overview of the history of the Balkans. It is no longer clear why these small states started to exist. The book explains there were geographical reasons for the original countries to come into existence. At some stage many of the people of the Balkans just thought of themselves as Greek. The idea of national states in the area is relatively new and has caused a lot of bloodshed.