I call BS. The Serbs invaded Kosovo. Get your facts straight. Excuse me, but you are wrong. Serbia didn't invade Kosovo. Kosovo has been part of Serbia for about 800 years. It was 90% Serbian until Hitler removed the Serbs and brought in Albanians, making the area majority Albanian. The removed Serbs lost everything when the Third Reich rounded them up and forced them out.
The KLA was financed and trained by the Albanian government. It was also partially manned by Albanian citizens. The Albanians and their puppets in Kosovo were the aggressors not the Serbs who were defending their country.
Serbia as a state hasn’t existed for anything like 800 years. It wasn’t until 1912-1913 that most of Kosovo came under Serbian rule - and “rule” seems to be the right word. As for being 90% Serbian, during the period between the World Wars there were certainly plans to produce this situation by driving ethnic Albanians out and replacing them with Serbian settlers. But these plans were not implemented (no doubt because Yugoslavia had bigger problems) and the actual population remained predominately Albanian.