Here's an excerpt from the Albania country study section entitled The Balkan Wars and Creation of Independent Albania:
"In July 1913, the Great Powers opted to recognize an independent, neutral Albanian state ruled by a constitutional monarchy and under the protection of the Great Powers. The August 1913 Treaty of Bucharest established that independent Albania was a country with borders that gave the new state about 28,000 square kilometers of territory and a population of 800,000. ... The treaty, however, left large areas with majority Albanian populations, notably Kosovo and western Macedonia, outside the new state and failed to solve the region's nationality problems".
And later: " Albanians claim Kosovo based on the fact that their kinsmen have constituted the vast majority of Kosovo's population since at least the eighteenth century".
And in the Yugoslavia country study: " After the mid-eighteenth century, Albanians became a majority in Kosovo "
Census data shows that the Albanian population of Kosovo was pretty consistently at 2/3 of Kosovos population for most of the century, although it was probably higher than that prior to 1913. The Albs were not happy about the Serbian takeover and revolted. In a manner familiar to anyone who followed the Kosovo situation in 1998-99, the Serbs brutally put down the Albanian resistance, so there was a drop in the Albanian population in the WWI period.
There's some illuminating comments from the Report of the International Commission to Inquire into the Causes and Conduct of the Balkan Wars Published in 1914 by the Carnegie Endowment for International Peace:
p.158 "They [the Servians] have resumed possession of their ancient domain, Old Servia proper (Kosovo Pole and Metchia), despite the fact that this historic domain was strongly Albanian." and p. 148 ... war is waged not only by the armies but by the nations themselves. "The populations mutually slaughtered and pursued with a ferocity heightened by mutual knowledge and the old hatreds and resentments they cherished. the object of these armed conflicts, overt or covert, clearly conceived or vaguely felt, but always everywhere the same, was the complete extermination of an alien population." and p. 149 "[as a result] the Albanian population [suffered] at the hands of the Servians."
Still, the 1921 census by the Kingdom of Serbs, Croats and Slovenes shows that 65.8% of Kosovo's population was Albanian and 26% was Serbian. That is considered by many scholars to be an undercount of the Albanians based on Albanian reluctance to be identified for either military conscription or for paying taxes.
The 1939 census show that the non-Slav population (ethnic Albanians, Turks, Gypsies, etc.) numbered 422,828 people, or 65,6%, the native Slav population accounted for 25,2% and the settlers (mostly Serbs) for 9,2%. (Settlers refers to the Serb colonisation program; a plan to increase the Slavic population in Kosovo and parts of Macedonia by bringing in Serbs from elsewhere and giving them confiscated Albanian lands).
In 1948, Serbs were 23.6% of the population, while in 1981 they stood at only 13.2%. Because ethnic Albanians boycotted the last census in 1991, there are only estimates of the population's ethnic breakdown for that year: Albanians, 81.6%; Serbs, 9.9%. Nacionalni sastav stanovnistva SFRJ (Belgrade: Savremena administracija, 1991) and Bilten No. 1934 (Belgrade: Savezni zavod za statistiku, 1992).
The Serbian government's Kosovo Coordination Centre's web-site used to have a census table going back to 1921, but it has vaporized--it reflected Albanian majorities in Kosovo prior to WWII & that is a very politically inconvenient truth in Serbia. Here's a hard-to-read table from the UNMIK web-site that shows post WWII figures:
Table 1.1: Total Population and Population by Ethnic Origin According to Population Censuses
Year Total Alb. Serbian Others
1948 729000 68 24 8
1953 808000 65 23 11
1961 964000 67 24 9
1971 1244000 74 18 8
1981 1584000 77 13 10
1991 1956000 82 10 8
So, liberal claim "Kosovo, province of Serbia whose 90% Albanian population favors independence" was a big, fat lie?
More than 225,000 Serbs were ethnically cleansed in the presence of NATO troops in 1999, and some 100,000 remained in Kosovo.
If Serbs were indeed only 10% of Kosovo population (225,000+ 100,000), that would mean that total Kosovo population in 1999 was over 3 million.
This is of course nonsense.
The lie about Kosovo being 90% Albanian was made to justify the bombing and hide subsequent NATO-sponsored ethnic cleansing.