The following map was issued in book "Yugoslavia, a Country Study", a publication printed by Headquarters, Department of Army, U.S. Government Printing Office, Washington, DC, Edition 1982, page 99. The subtitle for the map is:
Principal Languages and Religions
Note that this map talks about religious - not ethnic groups. A decade later "Muslims" from the map will be called "Bosniaks" in the Western press. Note also that Serbo-Croatian language is spoken by Serbs, Croats and "Muslims" (i.e. Serbs and some Croats who converted to Islam).
Compare this map with the maps issued by Encyclopedia Britannica, Edition 1990 and National Geographic, August 1990. The maps show basically the same configurations of the ethnic groups. Most of all, note that "Serbian Orthodox" - here - spreads far to the West from Serbia proper and takes sizable portion of Tito designed "Croatia" and "Bosnia and Hercegovina". These Eastern Orthodox Serbs who reside in these areas at least four centuries, as majority population, would be called by the Western media - "conquerors", "landgrabbers", "aggressors" etc. for the mere fact that they defended their own houses and property.
NOTE: The country of Yugoslavia was formed in 1918. Its first name was the "Kingdom of Serbs, Croats and Slovenes". Those three nations were the constituent nations of Yugoslavia. Thus, they have the right to (using peaceful means) negotiate leaving the union.
Albanians of Kosovo are NOT constituent nation of Yugoslavia. They are minority in the true sense of the term. To make a precedent and give Albanians of Kosovo "right" to secede would open a whole new Pandora's box in the international relationships.
[ Ethnic maps of Yugoslavia ]
[ Communist Yugoslavia ]