Check the historical conflict between Macedonia and Bulgaria. Bulgaria claims Macedonia was always part of Bulgaria, then split off, so they recognized them as an independent country and that was it. Macedonia claims all figures from the region as Macedonian, and calls itself the predecessor of the entire region. They also are highly aggressive against Bulgarians and call them fascists' and oppressors.

All in all sad sight. The smaller the countries, the weaker, the more similar, the more adversarial are they towards one another. It's like a pathological sibling relationship. There's dissonance and each one is fighting to "set the record straight" and dominate.