Yugoslavia was Tito. Once he died that house of cards came tumbling down. And Yugoslavia was predominantly Serbian-dominated even if Tito himself wasn't Serbian. Do you think that kind of arrangement could've lasted long? Honestly, this isn't multiculturalism as was the Austro-Hungarian empire. This was a bunch of people with long-held grudges forced to live together under quasi-socialism (there was a decent free market, at least decent for a socialist country). Also, Yugoslavia was for South-Slavics, not Slavics in general. Croatia wanted its own thing (NDH) but the whole Hitler failing thing kind of made a dent into their plans.