I have a difficult time finding information on this conflict that does not appear biased. It seems much more difficult to see who was at fault compared to a conflict like WWII (I know history is not black & white, but it's hard to argue against the allies being, as a whole, preferable to the axis. The same cannot be said about the Yugoslav conflict). Much of the information seems to be anti-Serb, but other sources point towards international actors or Croats as the antagonists. I understand the history of conflict in the region goes back millennia, but I am primarily looking at the modern history leading up to the war.
The war ended in 1995 but began earlier than that, so I hope this does not violate the 20 yr rule.
Going back a ways, it was sparked by the death of Josip Tito, who had kept Yugoslavia unified for decades due to his overarching support amongst all ethnic groups. After his death, things started to fall apart as ethnic tensions emerged once again as his successors mismanaged Yugoslavian affairs. Croatia and Slovenia were richer than the rest of the "nations" which were supposed to be equal within Yugoslavia, so there was a degree of resentment against them. Additionally, both Serbs and Croats had committed atrocities against each other 50-70 years before, and the resulting tensions were buried in a shallow grave.
Separatist tendencies arose in Croatia and Slovenia, while Serbian nationalism was also on the rise. Serbians eventually took majority control of the Yugoslav government, which ultimately led to the boycott of the National Assembly by Croat and Slovene officials. This allowed Serbia to do pretty much whatever they wanted. Slovenia split off after the fall of Communism, followed by Croatia. Since Croatia was home to much of Yugoslavia's wealth, the rest of the country was not about to let it go.
MarshalOfNewZealand's response is also correct for how international interests came into play. The cutting of foreign funding and the allure of capitalist European economic prosperity was largely the impetus for Croatia's declaration of independence.
My source is the book "Blood and Vengeance" by Chuck Sudetic, which I read for a class on Yugoslavian history last year.
The collapse of the Soviet Union suddenly meant that the United States no longer had need for the neutral buffer state that Yugoslavia was in the middle of Europe.
As a result, living standards decline, and ethno nationalism increases as the peoples of Yugoslavia felt they would do better independent rather than under the Belgrade authorities, whom obviously wished to preserve the union.
Combine this wish among the republics to separate from Yugoslavia with an equally strong wish in Serb/Croat populated areas to separate from the newly independent states (of Bosnia and Croatia) and support (both military and political) offered from Western Europe to the newly independent republics and their "right to Territorial integrity" (which wasn't afforded to Yugoslavia) and you have the recipe for disaster that followed