I know the people used to live in relative peace in Yugoslavia before the civil wars. My parents are serbians who grew up in Yugoslavia before the wars and I was born in Australia just as they were happening. They told me there wasn't that much hatred as they were growing up until they left in '86 or so. But they were from Nis which also wasn't as badly affected by the wars and is very homogenous.
Watching the amazing 6 part documentary by BBC The Death of Yugoslavia it seems like there were so many populist uprisings in favor of racism and nationalism. I'm trying to wrap my head around the massive change in ideology and can't think of much other than a rather simplistic explanation of a poor economy - but it seems much deeper than that.
Would love if anyone could shed some light.
If I'm not mistaken, this dates way back to the independence of Serbia, which wanted to unite all 'Serbs' (South/Balkan Slavs) into the medieval notion of Greater Serbia, or what is now known as Yugoslavia. The 19th century was a century with the rise of nationalism, and the rise of nation-states (like Germany and Italy) plays into that. Serbs wanted the Croatians and Bosnians to be part of their united state, even if it meant ripping them away from Austria-Hungary and fighting Bulgaria over Macedonia.
I'm not sure I answered your question, but from what I've read, this isn't something unique to the collapse of Yugoslavia, but rather something that has existed since the breaking apart of the Ottoman Empire (and even before that I believe, as the notion of Greater Serbia was brought along in the later Medieval by a Serbian king named Stefan something, don't have the source with me unfortunately).
source : The Sleepwalkers, by Christopher Clark, chapter Serbian Ghosts
Some of it might have been due to economics. The Yugoslav economy collapsed in the 1980s. "There was a sharp stop in the growth of the Yugoslav GDP in 1980, and its decline began around 1986," according to the Ludvig Von Mises Institute Canada. So right around the time your parents left.
I would suspect that that left people feeling more adrift and desperate, especially as the rest of the world became more prosperous right around that time (economic expansion in Western Europe and North America in the late 80s). Together with the collapse of communism that opens a leadership void which can easily be exploited by charismatic nationalistic politicians, which is kind of exactly what happened.
Source: https://mises.ca/posts/articles/the-economy-of-titos-yugoslavia-delaying-the-inevitable-collapse/
I'm rather short on time now, and have posted multiple times before on similar questions, so I hope you won't mind if most of this reply consists of links to other discussions.
Here is a recent one, also inspired by The Death of Yugoslavia which is mostly about Yugoslavia after Tito and the legitimation of power. Tl;dr would be that as socialism lost its legitimation power, nationalism replaced it. Some sources for that view would be Ramet, Three Yugoslavias and Jović, Yugoslavia: A State That Withered Away.
History of the Balkans AMA had some rather large discussions on both Yugoslavia, including wars.
Here is a bit more about fall of Yugoslavia. Nationalism is not a major topic of that thread, but inevitably it has a role.
You might also find interesting this post about how wars are popularly interpreted now in different parts of ex Yugoslavia However, that one is much more based on my personal experiences in those areas than any systematic studies.
Posts here are more on the economy, but again nationalism has its place
I apologize for not writing anything original or specifically suited to your question, but I hope those old threads might answer most of them.