Kosovo was under Ottoman rule until the First Balkan War in 1912. After the war, Serbia was hoping to annex what is now northern Albania to get access to the Adriatic Sea, but Austria and Italy were opposed to Serbia having a coastline on the Adriatic. Austria apparently wanted Kosovo to be part of Albania. It was because of support from France and Russia that Serbia got Kosovo then (except for a small portion which went to Montenegro, but later went to Serbia when Tito redrew the borders after WWII).
It was because of support from France and Russia that Serbia got Kosovo
Kosovo was part of serbia after 1912 1st balkan War, so Serbia went into WWI WITH Kosovo And Vardar Macedonia( as integral parts of Serbia)
Commie Tito actually started separation of Kosovo FROM Serbia giving it authonomz, and later more and more ceeding it from Serbia, up until 1990.