By the way, looking at the info under "Bulgaria", I noticed that Bulgaria was always in the way of Greece and vice versa and they always have been adversaries.
Basil the II of the Byzantine was nicknamed "Bulgar-Killer" and he's is a huge hero of the clashes between the Bulgars and the Byzantine Greeks.
Later Bulgaria and Greece fought in the Balkan Wars. Finally in both WWI and WWII, Bulgaria sided with the Germans. So that's where some of the hostility is generated from. We have never been in good terms.
There's the general idea that the Bulgars were barbaric hordes and extremely vicious, even worse than the Ottomans were - at least the Greeks coexisted with the Turks for some 400 years. That is my guess, I never paid attention at school.