Quoting Wikipedia [1]: "The Balkan Wars (1912–1913) and World War I (1914–1918) left Ottoman Macedonia divided between Greece, Serbia, Bulgaria, and Albania and

Quoting Wikipedia [1]: "The Balkan Wars (1912–1913) and World War I (1914–1918) left Ottoman Macedonia divided between Greece, Serbia, Bulgaria, and Albania and resulted in significant changes in its ethnic composition. The immediate effect of the partition of Ottoman Macedonia were the nationalistic campaigns in areas under Serbian and Greek administration, which expelled Bulgarian churchmen and teachers and closed Bulgarian schools and churches. As a consequence a sizable part of the Slavic population of Greek and Serbian Macedonia fled to Bulgaria or was resettled there by virtue of a population exchange agreements. The Bulgarian population in Vardar Banovina was regarded as "Southern Serbs" and a policy of Serbianization was implemented. Within Greece, the Southern Macedonians were designated "Slavophone Greeks". [1] https://en.wikipedia.org/wiki/Macedonian_Bulgarians https://en.wikipedia.org/wiki/Macedonian_Bulgarians