Also, it’s very misleading to think of Serbs and Montenegrins as “practically the same people”. For example, if you compare Serbs from Vojvodina (just south of Hungary) and Orthodox Montenegrins, the differences are vast. In culture, dialect, ways of thinking, etc.
Serbs and Croats in Vojvodina and Slavonija are much more similar. Other than religion, they are in all other aspects very much the same people.