Take your propaganda elsewhere. The certainty that you display is not backed up by the facts. Here's just one unbiased source: http://lamar.colostate.edu/~grjan/kosovohistory.html
The earliest known inhabitants of Kosovo were called Illyrians by both Greeks and Romans. Albanians today claim to be direct descendants of the Illyrians. Serbian scholars claim that Albanians appeared on the scene in the early Middle Ages as a result of intermarriage between nomadic shepherds and unromanized remnants of Illyrians and Dardanians from Thrace. Tracing such descents is difficult but the people living in the region before the arrival of the Serbs from the North are likely to have some genetic relationships to Albanians, but DNA data would be needed to definitively settle the claim, which in any case is hardly germane to the current conflict. The region was conquered by Alexander the Great 300 years before Christ and became part of the Roman province of Dardania in the 4th century A. D.
Notice that the facts of who the first inhabitants were is in dispute, not cut and dry like you said. Similarly, these disputed facts are not germaine, so your claim that Kosovo belongs to the Albanians based on their being the first inhabitants is not relevant.
Again, I say if you want to propagandize, find a different forum to do it on.
That of the Serbs, who sometimes have the gall to say that they were the first inhabitants of Kosovo whereas they are only its third known invaders.
That of the Romanians, who know that their language is related to Albanian, and want to claim as their ancestors the Dacians, a Thracian tribe north of the Danube, notably to bolster their territorial claims on Transylvania.
You didn't mention the Thracian thesis, dear to 19th century balkanologist Gustav Weigand, but it is the only alternative to the claim that the Albanians are indeed the descendants of the Illyrians. Or used to be, since it is now established that the Bessi, the only Thracian tribe which had retained its language in the 6th century, were exposed to Christianity in their own language, whereas it is obvious that the proto-Albanians received it in Latin.
There is much more evidence, notably archaeologic, that the Illyrians were indeed the ancestors of the Albanians, and those who deny it now are acting in bad faith.
Now if you consider first ownership to be irrelevant to the issue of legitimate property, it only proves that you are a bad political philosopher as well as an ignorant in Balkan history. The fact that I am not does not make me a propagandist: it only enables me to refute you without using any documentation. To paraphrase your arrogant formula: take your incompetence elsewhere. What is wrong about knowing what one is talking about?