If I may give some suggestions for this map. I love it, but you have missed some points:
1. In SFRJ, Kosovo and Vojvodina were provinces of Serbia (and what you named "Serbia" was "Inner Serbia"). You could put "greater" bonus for holding whole Serbia (Inner Serbia, Vojvodina and Kosovo)
2. There isn't river between Syrmia and Slavonia. River Danube and Tisa divide Vojvodina in 3 regions: Bačka (between Danube on west and south, Tisa on east and Hungarian border on north), Banat (between Tisa on north-west, Danube on south-west and south, Romanian border on east and Hungarian border on north) and Syrmia or Srem (between Danube on north and east, Croatian border on west and Sava river on south).
You could just put Danube and Sava as rivers and maybe Morava
Your division of Vojvodina is ok, but you have made few mistakes with bridges:
-Slavonia and Syrmia are bordering and that border should be crossable
-You should put Danube between Bačka, Syrmia and Banat with bridge only between Bačka and Syrmia
-There should be bridge between Slavonia and Bačka (or Novi Sad how you named it)
-There should be bridge between Syrmia and Belgrade as bridge "Gazela" is one of the most crossed bridges in Balkans (it connects Syrmia and rest of Serbia)
-There is a bridge between Belgrade and Banat, but you could eliminate it to keep game interesting
3. You divided Bosnia and Herzegovina as it is now divided (between Federation of BiH entity and Republic of Srpska entity). Until 1992. regions in B&H were a bit different. In my oppinion you should have made regions: Posavina (North BiH, by river Sava), Bosanska Krajina (western BiH), Cazinska Krajina (north-west of BiH, bordering Croatia), Podrinje (eastern BiH), Herzegovina (southern BiH) and Central Bosnia (perhaps dividing it into Tuzla and Sarajevo)... something like
this map4. Your region "Podrinje" should me renamed to "Mačva" or "Šumadija" if you extend it a bit more
Those are my suggestions, if it's not too late for editing the map