Kosovo is a part of Serbia that has a large significance to the country mostly because of the cultural heritage and history.
Serbia and Russia are Orthodox countries, and Kosovo is known for many Orthodox monasteries that were built there in the middle ages. The center of the Orthodox church was in the Patriarchate of Pec and therefore it has large religious significance for both countries, especially Serbia. Additionally, it was also a part of its territory for decades and therefore they don't want to give up on it.
