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Where to start, since the factors are incredibly numerous and whoever tries to tell you a one-dimensional or simplified version, is pushing an agenda (of whichever nationality within ex Yugoslavia). Story has to be told in full. In very short TL;DR before i continue, the factors can be summed up to - increased confederalization of the country during and after Tito, Tito's death, failure of economy and simultaneous rise of Albanian, Serbian, Slovenian and Croatian nationalism through the 1980's, and the fall of communism in Europe in 1989-1991, as well as introduction of a multiparty system which was along the republic lines.

- For many people the usual starting point is 1980 and the death of Tito. But the basis for dissolution can be found much earlier, in the 70's. In 1971, after 25 years of existence, Yugoslavia experienced the first outburst of nationalism within its borders, so called ''Croatian spring'' openly opposing unionization of the country, by Croats. This is an important event because it effectively marked the death of an idea of unionist, ''Yugoslavian Yugoslavia'' (remember, Yugoslavia also had ''Yugoslavian'' as an ethnicity in the census, with the plan that one day most of the Slavic population marks themselves as that, but it was never achieved, not even close). From that moment on, it was clear that the federation was the maximum level of unity Yugoslavia could achieve, and that despite everything, national/ethnic interests were still strong and would remain so.

- In 1974, after many years and a lot of debates, new constitution was created - it started the trend of disuniting the country, because the constitution introduced a concept that sovereign rights were exercised by the federal units (republics), and that the federation had only the authority specifically transferred to it by the constitution. Moreover, two autonomous provinces, both located in Serbia (Vojvodina and Kosovo) were effectively given a status equal to the republic (though remaining provinces), being taken out of the Serbian sovereignty. This was extremely controversial in Serbia and let to protest from many intellectuals including the famous ''walk out'' out of Belgrade University Faculty of Law in 1974, which ended in many professors being fired. Beside the stated problems, constitution itself was incredibly cumbersome, badly written and generally complicated. Same as the ''spring'' stoked the earliest sparks of reborn nationalism in Croatia, this did the same in Serbia.

- In 1980, Tito died without effectively leaving the system to succeed his position. He was succeeded by the ''presidency'' made of representatives of every republic and autonomous province. From this point on, Yugoslavia was effectively more of a confederation than a federation, and the trend will only continue during the 1980's.

- In 1981, in Kosovo, Yugoslavia's poorest region, Albanians started the rebellion, which marked the first ethnic nationalist uprising in Yugoslavia (Croatian spring was more in the form of protest and cultural manifestations - Situation in Kosovo led to rioting, arrests, and emergency situation). Moreover, Serbs in Kosovo felt that situation wasn't handled the way it should have, and longed for the return of the province under the full control of the republic as it was before 1974. This kind of domino effect of nationalism would appear in most events in Yugoslavia.

- Parallel with all this, economy should be mentioned before i move on - by late 1970's, economy started stagnating, even occasionally falling into recession during the 1980's, before collapsing in the late 1980's.

- In 1987, Slobodan Milosevic was elected as the Chairman of the Serbian Communist Party (Branch of the League of Communists of Yugoslavia - see, even the ruling party was confederalized and separated by republic lines). Appearing as the populist strongman, he vowed to calm the situation in Kosovo. In the worst timing ever, in 1989 came the 600 year anniversary of the Battle of Kosovo (1389) which is one of the central elements of Serbian patriotism, art, epic poetry and national consciousness. On the anniversary day, 28 of June, Milosevic held a huge gathering on the site of the battle, which attracted hundreds of thousands of Serbs. This symbolically marked the moment Serbian nationalism was woken up.

Parallel with all that, Slovenian separatism was slowly rising through the 80's. with the different cause - Slovenia was the most prosperous republic, closest to European Community and least hit with the economic troubles of the 80's. As the idea of Yugoslav unionism slowly waned among all nationalities, Slovenians were the first to take effective measures of leaving Yugoslavia.

In the unfortunate timing of communism falling in Europe, the League of Communists held the 14th Congress in January of 1990. Congress's goal was to determine the future of the country. Serbian delegates led the ''unionization'' faction, while Slovenian delegates led the ''confederalization'' faction. The congress, in short, was a total mess, and ended with Slovenian delegates walking out - this marked the end of the League.

In the aftermath of the congress, it was decided that multiparty system would be along the republic lines. Through 1990, republics had their elections, starting with Slovenia and Croatia and ending with Serbia and Bosnia. In Slovenia and Croatia, nationalist separatist parties won. Bosnia is a complicated story because it's effectively a ''Small Yugoslavia'' with three ethnicities each giving their representative - but anyway, among the Bosniaks and Croats, separatist options also won. In the rest of republics, unionist parties gained the power (usually transformed communist parties) while nationalist options were in opposition (this was true for Serbia too, where SPO, the party propagating Greater Serbia and monarchy actually won only 16% of votes).