As for Kosovo, it is a historical place for Serbs (just like Thermopyles are for Greeks). In 1389 there was a war between Serbs and Ottomans in Kosovo, and Serbs lost. Some years ago however, Albanians started to kill Serbs in Kosovo and NATO backed Albanians up. The majority of Greeks (including me and my family), support Serbs on this matter, but I fear Trump is rather unable to return Kosovo to Serbs.
Should we also return Greece to Italy then? It was once part of the Roman empire after all. Of course, there are almost no Italians living there, but that's not much different from the Serbs in Kosovo. (Yes, the comparison is exaggerated and the situation is more complicated than that, but with 92% Albanians and 4% Serbs, it's not clear that returning everything to Serbia is a good idea.)
Greece to Italy?
Nazi Italy and its war with Greece just shows how genocidic Italians are.
Through, Athens, Sparta, etc, etc were there before Italy.
92% albanians on Kosovo? Could be easily solved! You just decline all healthcare, free education to Albanians, .rs domain, +381 number, and they start returning to Albania. Then, you give minimum 3 children to be born on Kosovo per mother, give better pays in Pristina than in rest of Serbia, and people start migrating to Kosovo, and eveything is alright! Then, remove better pays and make minimum 3 children to be born in whole Serbia, you populate it up to 12 million and done.
USA is Spanish/Britain colony which did not had any direct war except with Canada, making black people slaves and then succeed into good country!