What happened was that the Yugoslav staes were set up ith a rotating presidency by Tito the idea being that one state would not be favoured over the interests of the others.
This meant that each state took it in turn to govern but when it came to Croatia’s turn they announced before the handover that they were going to secede once they held the reins of power.This could only be done if there was mandate from the population so a vote would have to be held.
Franjo Tudjmann was Croation state president at the time and realised that the necessary majority would not be realised since there were a large number of ethnic Serbs living in certain provinces, most notably Krajinya.He then started to come up with citizenship rules that would disqualify certain individuals, naturally the most affected woud be the Serbs in Croatia.This was aided by the fact that all Yugoslavs had their ethnicity recorded on passports and other official documents.
Slobodan Milosovic, in the meantime, had seen all the communist power structures in nations around him fall and had disguised himself as a populist electable politician.
The economy was becoming weaker due to the uncertainty and he needed a cause to draw his power base, the ordinary Serb, around him.
One thing he did was to hang on to Presidency of the Yugoslav federation well beyond the alloted span on the grounds that it was illegal to break up Yugoslavia thus denying Tudjmann the means to call a vote in his state.
Milosovic campaigned on a wave of nationalism that Serbs in Krajina were being persecuted (they were having their voting rights denied in truth) but this was a gross distortion.
Milosovic then called on all Serbs to fight for a creation of a homeland which alarmed all the other states since at one time or another almost every bit of land had been disputed and led them all to think that he was on the path to creating a Greater Serbia - in other words empire building.
Certain states such as Slovenia and Montenegro made no noises about leaving the Yugo Federation as there was no way they could have done so.
Add to this that Slavonia had already decided to leave no matter what the outcome over the wrangling over the Federation Presidency and Milosovic had the evidence he needed.
The first thing that was done was to equip local militias with weapons which the Serbs did, but only for their own grouping.
The Slavonians had seen which way things were going the moment Tito died and had been re-equiping their police very early on and training them, they effectively became an army.
The Croats took a long time to realise the implications and Bosnia as such was hardly recognised by either the Serbs or the Croats as a separate entity, in fact that area was to be the subject of a land grab.
The thing about the distribution of various populations was that there was many areas that were within say Croatia that had majority Serbs and vice versa so there was a process of removing those inhabitants - ethnic ‘cleansing’ murder intimidation and every evil that can be visited on a person.
Meantime Milosovic sent his army over into Slavonia to prevent its secession by force.
Slavonia is well known for its very steep valleys and few main roads, all the Slavonians did was to wait until the Serbs went into those valleys and simply bottled them up, tactically the Serbs were completely sunk, the Slavonians could destroy then at their leisure and with long and difficult supply lines a military disaster would have been inevitable so they surrendered with hardly a shot fired.
Even Milosovic was surprised by the tactical skill of the Slavonians and their preparations.He was forced to acceded but on Slavonias terms.
Milosovic was forced to announce that since Slovenia was ethnically completely differant to the rest of the federation and that Slavonias interests lay with Italy and Germany they would be allowed to leave.
Humiliated Milosovic unleased his militias in Krajina privince and wrested it from Croatia.It was during this phase of the war that Dubrovnik was severely damaged.
From here ethnic cleansing was accelarated drastically with gross atrocities on all sides and the three way war with its odd mix of local alliances between the Serbs Croats and Bosnians took off.
I’m not sure how Macedonia (Skopje) broke away but I would have thought that Milosovic did not want to upset Turkey as they could quite easily have cut off supplies along the Danube.
Eventually the West realised how dangerous things were becoming and began to support and train Bosnians and the Croats. The West took Croatia’s part, even though it had hardly behaved any better than Serbia over atrocities and the Russians took Serbia’s part.
Russia had enough of its own problems and slowly backed away from Serbia after huge pressure from the US.
Serbia was effectively isolated from the rest of the world by sanctions and it began to tell.
When or what the agreement was that caused Serbia to withdraw its support from the Krajina Serbs is not yet public knowledge but likely entailed the recognition and inviolability of its own borders.
Just how vulnerable those borders were was demeonstrated by the swift retaking of all the land they had taken from Croatia in a brilliant strategic move which saw a large numger of Serb troops cut off and the Vokovar area restored to Croatia.
The Croatian army grew up.
Slovenia took the weakness of the Serbs as their best chance to break away, which they did and Serbia had no response, which is why there was so little bloodshed.
Serbia never let anyone try to break away but they simply were never in a position to do anything about Slavonia, or Slovenia, and I’d guess Macedonia.
Its a a sobering thought that all Milosovic did was make promises, and lose 4 wars in succesion yet still it took a coup to get rid of him.