From Postwar: A History of Europe Since 1945, by Tony Judt (Penguin, 2005), pp. 670-671:
Kosovo had historic significance for Serb nationalists as the last holdout of medieval Serbia against the advance of the Turks and the site of a historic battlefield defeat in 1389. The local Albanian predominance was thus regarded by some Serb intellectuals and politicians as both demographically troubling and historically provocative—especially since it echoed the Serbs’ displacement by Muslims as the largest minority in the adjacent Bosnian republic. Serbs, it appeared, were losing out-to hitherto subservient minorities who had benefitted from Tito’s rigorous enforcement of federal equality. Kosovo was thus a potentially explosive issue, for reasons linked only tenuously to ‘age-old’ Balkan feuds….
Whereas Serb dislike of Albanians fed on proximity and insecurity, in the far north of Yugoslavia the growing distaste for feckless southerners was ethnically indiscriminate and based not on nationality but economics. As in Italy, so in Yugoslavia, the more prosperous north was increasingly resentful of impoverished southerners, sustained—as it seemed—by transfers and subsidies from their more productive fellow citizens. The contrast between wealth and poverty in Yugoslavia was becoming quite dramatic: and it correlated provocatively with geography.
Thus while Slovenia, Macedonia and Kosovo all had approximately the same share (8 percent) of the national population, in 1990 tiny Slovenia was responsible for 29 percent of Yugoslavia’s total exports while Macedonia generated just 4 percent and Kosovo 1 percent. As best one can glean from official Yugoslav data, per capita GDP in Slovenia was double that of Serbia proper, three times the size of per capita GDP in Bosnia and eight times that of Kosovo. In Alpine Slovenia the illiteracy rate in 1988 was less than 1 percent; in Macedonia and Serbia it was 11 percent. In Kosovo it stood at 18 percent. In Slovenia by the end of the 1980s the infant mortality rate was 11 deaths per 1,000 live births. In neighbouring Croatia the figure was 12 per 1,000; in Bosnia, 16 per 1,000. But in Serbia the figure was 22 per 1,000, in Macedonia, 45 per 1,000 and in Kosovo, 52 per 1,000.
What these figures suggest is that Slovenia and (to a lesser extent) Croatia already ranked alongside the less prosperous countries of the European Community, while Kosovo, Macedonia and rural Serbia more closely resembled parts of Asia or Latin America. If Slovenes and Croats were increasingly restive in their common Yugoslav home, then, this was not because of a resurfacing of deep-rooted religious or linguistic sentiments or from a resurgence of ethnic particularism. It was because they were coming to believe that they would be a lot better off if they could manage their own affairs without having to take into account the needs and interests of underachieving Yugoslavs to their south.