'The Death of Yugoslavia' (Laura Silber and Allan Little) answers both these questions pretty decently in it's preamble up to the actual rise of Milosevic, apologies for the block of text:

"Throughout his stewardship of Yugoslavia, Tito worked to prevent his state from suffering the same fate as it's predecessor - from falling under the hegemony of the biggest nation, the Serbs, who were twice as numerous as the second biggest, the Croats. Successive post-war constitutions were designed to balance institutional power between the republics, as a way of spreading power among the nations.

In his eternal battle to keep the nations on an equal footing, Tito ruthlessly suppressed any expression of resurgent nationalism. Enforcing his doctrine of 'Brotherhood and Unity', he carried out purges of Serbs, Croats, Muslims, Slovenes, Macedonians and Albanians, balancing his repression of any one nation against that of the others. Nationalists were jailed or sent into exile, where resentment nurtured in expatriate communities as breeding grounds for extremist nationalism.

Tito was frequently likened to a great old oak tree, in the shade of whose immense branches nothing else could grow. In his last years in the late 1970's, no heir apparent emerged. Wary of appointing a successor, Tito created a hopelessly inefficient inheritor of his mantle: the collective head of state to replace him was an eight-member, annually rotating presidency (who would also serve as army commander-in-chief), comprising of one representative each of the six republics and one from each of Serbia's two autonomous provinces, Vojvodina and Kosovo.

When Tito's health began to deteriorate, federal institutions deteriorated with him. Yugoslavia became a country composed of little more than 8 regionally-based and separate Communist parties, the secret police and the army. When he died at 88 in May 1980, there was a genuine outpouring of grief among all of Yugoslavia's nations. The Albanian Communist, Mahmut Bakalli, later remembered: 'We all cried, but we did not know we were also burying Yugoslavia'."

To go more into that second question:

• As recounted above, Tito entirely failed to set up an appropriate succession, and so the centralised, strong control over the nation became a jumbled mess of separate regional/political interests.

• Over the decade following Tito's death, calls for democratisation became too strong to ignore, and nationalist groups who directly countered the 'Brotherhood and Unity' doctrine swarmed the republics.

• Without so harsh an eye, those expatriate communities began to spread back to their roots a bit, furthering this nationalist uprising. Yugoslavia's survival was to a large extent dependant on it's citizens belief in a Yugoslavian identity going over the more established national identities, hence why this political shift was so damaging to the core of the nation.

• Tito was clever in playing Yugoslavia's position in the Cold War as a non-Moscow Communist open to aid from both sides, especially the USA. A decade after his death, the Cold War was in it's death knolls, and with it much of Yugoslavia's geopolitical significance and any aid it was receiving from this. With any slump comes discontent, and it coincided with the nationalist movements rise to prominence in a perfect way to sow chaos.