Not only do you have a large Muslim population–and while it seems to have been mostly supplanted by Chechnya in the popular consciousness, Bosnia-Herzegovina has been a prime recruiting ground for Al Qaeda, Jabhat al-Nusra, and Daesh–but increasingly Russian, European, and Chinese interests have turned toward the Balkans.
It is still possible that a flare-up in the Balkans now would see Russian, American, and European intervention–with the PRC playing their shadow games the whole time–and without overt flare-ups. It could well be a very close thing, however. It might not see the complete US-European breakdown that comes to a head in Escalation, but there are quite a few reports of harassment and provocations between US and Russian forces in Syria. And with the US largely backing Kosovar interests while the Russians have long backed Belgrade…
Picture this in the Balkans, with a whole lot of other pressures built up:
None of this is saying that if the Fourth Balkan War happens, that it will necessarily be the flashpoint that triggers the next world war. Just like any flashpoint with multiple outside interests involved, the potential is always there. And the realities of Fourth Generation Warfare make it harder to see just when that war might kick off.
Presuming it hasn’t already.