Disclaimer

Firstly let me say that I grew up during Slobodan regime in a family that disliked his policies and I more or less share that opinion with my parents. That being said I will try to be objective as I can, even thought his policies had negative influence on my life.

Although Sloba(common nickname for Slobodan, that is how he is known in Serbia) was born and grew up in Požarevac, Serbia. His parents were from Montenegro, clan Vlasojevići. Later he used this fact to score political points in Montenegro and gain popular support. Fun fact is that his father left his family while he was very young and that his mother raised him and his brother alone. His brother developed successful independent carrier in diplomacy.

During high school Sloba met Mira Marković, his future wife. She came from old communist family and her father Moma Marković was partisan and high ranking communist and so was her uncle Draža Marković who even held same positions in government as Sloba, 20 years earlier thought. Mira is the one that introduced Sloba to youth wing of LCY(League of Communists of Yugoslavia) and was driving force behind his politics during his presidency, always being by his side.

He studied law in Belgrade and finished as a top of his class. Also he showed himself as really good orator, another thing that would be useful in his political carrier.

During that time he met Ivan Stambolić, who was first his political ally and later enemy. Both Milošević and Stambolić were so-called next generation of communists. They weren't 'old guard' that joined party with Tito and went trough WW2 and revolution. They came to their position by climbing party ladder by working as functionary of 'self-managing' companies. Mostly banks, natural gas industry and chamber of commerce for Sloba and Ivan. They also didn't have as dogmatic view of communism as did older generations. Thing of noting is Sloba was know as Stambolović's lackey always filling in positions that Stambolović was leaving or were subordinate to him.

Eventually two pals quit their managing carriers and get high ranking positions in Belgrade firstly local and later even federal level. Eventually Stambolić would became President of SR Serbia and Milošević President of Central Committee of LCS.

However things in country start going to worse with economic crisis in the 1980s and with series of strikes, protests and incidents across the country. By far poorer areas were hit the hardest AP Kosovo, Montenegro and Macedonia but others as well. Kosovo was extremely volatile as it was ethnically mixed between Serbs and Albanians. Most notable of all incidents were: Paraćin massacre, where Albanian kid during his mandatory service in army killed four fellow soldiers. This was presented by Serbian media as attack on Serbs(only one of those was soldiers was a Serb) and protests against Albanians went on in Serbia just adding fuel to the fire. On Kosovo there was a strike by Serbs who demanded 'protection' from Albanians. Belgrade sent Sloba to appease situation but he instead made things worse and said his famous quote ''Niko ne sme da vas bije!'' ''None shall beat you!'' to Serbs that were fighting with predominantly Albanian police force. That quote was aired on TV and Sloba was seen as protector of Serbs. To high ranking Serbian communists this was seen as nationalistic statement and trouble especially Stambolić who was more moderate. Another crisis was when papers published leaked Serbian Academy of Sciences and Art Memorandum to the public. It was mostly nationalistic propaganda and one step before a call to Great Serbia where they stated that Serbs were being oppressed in Croatia and Kosovo and called for higher centralism.

8th session of CC of LC of Sebia was approaching and Stambolić was suspicious of Sloba's intentions so he sent a letter to members of CC of what should they do if Sloba suggest expulsion of Dragiša Petrović, Stabolović's ally and opponent of anti-Albanian sentiment that was rising in Serbia. He said in letter they shouldn't listen to Sloba and this proved a fatal mistake as during session they did that with large majority and few days later Stambolić had to quit his post as president of SR Serbia. This whole debacle was aired on national television. It wasn't that easy for Milošević to do this Stambolović was actually highly outmaneuvered. First Sloba filled committee with people loyal to him and not Stambolivić, used his misstep with the letter against him and by playing nationalistic card he was more popular than Stambolović.

Next step from Milošević was so called Anti-bureaucratic revolution where he replaced governments of AP Vojvodina, AP Kosovo and SR Montenegro and put in people loyal to him. This would turn to be crucial during 14th party congress. He also reduced autonomy of Kosovo much to the dislike of the Albanians. He tried to do this in other republics but failed. On 28th of June 1989 on 600th anniversary of Battle of Kosovo, major event in Serbian history and nationalistic ideology, Slobodan Milošević goes to Kosovo and has a speech in which he reinforces Serbian nationalism and calls for unity among Serbs but at the same time he praises diversity and calls Serbia Bulwark of Europe. To truly understand the speech you need to be familiar with Kosovo myth and that is a whole other topic.

However Croatian and especially Slovene politicians saw this for what it was rise of Serbian nationalism and call for centralisation of Yugoslavia and they would have none of it. Slovenia and Croatia were two most developed republics and they were burdened by economic failures of other parts of federation. Meanwhile as you know communism collapses in Europe and same thing happends in Yugoslavia or does it? First multi party elections were held in 1990 across Yugoslavia. In Slovenia and Croatia new democratic parties won. In Serbia Slobodan's party won which was just rebranded LCS. Thing is that most of media was state controlled and there was little coverage of other opinions.

You ask how did it take so little for 14th party congress to fail, it actually took a lot more: whole decade of economic crisis that was result of bad economic policy from Tito's time, desires by political Belgrade for centralisation so it could substitute their other shortcomings, change of generations in political life and failure to read political climate in Europe.

Why do you get impression of Yugoslavia as anti-nationalistic paradise? Country was made as nation state for South Slavs and is infamous for expulsion of Germans, Italians and Turks. Even before 1980s it was quite nationalistic each nation was given their own republic. When we talk about stopping national hatred in context of Yugoslavia it is meant hatred between nations of Yugoslavia.

P.S. I didn't mention Constitution of 1974 because it would make story even more complicated, also I mostly focused on happening in Serbia during this time there was a lot more going on on federal level and in each republic individually independently and as a reaction to happenings in Serbia. I also omitted some other things so that I don't break 20 year rule.

Sources/further reading By far best book is by a Croatian author

Dejan Jović: Jugoslavija - Država koja je odumrla/Yugoslavia - A State that Withered Away

Also:

Slavoljub Đukić - On, ona i mi

Aleksandar Andrić - Istorija Srbija 1918-2008

Aleksandar Andrić kinda comments on events that he witnessed but he is still good compared to others

The most important part of his coming to power is that he already had power. He was high ranking official of communist party, so he was politician with reputation and connections. He won on the first elections in 50 years. There were a lot of people in elections who were only familiar with him. Some of them didn't want anything to change and he was critical part of the old establishment. About second part of your question, I don't think he broke up Yugoslavia. He did a lot of really bad things, but breaking up of Yugoslavia took effort of all political leaders in it.