Yeah, and I would even push against the language being the main problem. Uniting people is hard because in order for all of them to adopt the same identity, they first need to adopt the same mythology of self, because that's all a nation is - it's a story, an abstract narrative most people believe in. First Yugoslavia actually had a good chance on the Croatian side, mainly because the Croatian national revival wasn't led by illiterate Croats but mainly by croatized and urban German, Czech and Slovakian intelligentsia, who already had a Yugoslav idea in mind with their Illyria myth. Ethnic Croats were primitive nationalists like everyone else in the Balkans. The problem was, even this elite wouldn't accept anything below the bare minimum of autonomy and our own parliament we'd already had in AU. Serbs immediately had other ideas as we know, so that country died before it even had a chance to develop its own mythology and the result was a Croatian nationalist counterstrike right at the time of the rise of Fascism. This led from viewing the Serbs as slavic brothers, to putting them into death camps within 20+ years.

After that quick genocide which caused a generational trauma in Serbs, 100x worse than anything they felt against the Turks, nothing has ever been the same nor will it be any time soon. The second Yugoslavia had been held together only as a Cold War dictatorial cordon sanitaire between East and West. As soon as the Berlin Wall fell we all knew another war was coming. So, we need to put these delusions aside and first need at least a couple of generations just to re-learn how to be good neighbors.