After liberation, internal Greek quarrels led to the outbreak of the Civil War. Northern Greece (Macedonia, Thrace, Epirus) because of its mountainous terrain and common borders with the Communist Balkan countries, became the center of the conflict.
The fighting was most destructive in western and central Macedonia, and a large number of citizens fled the war zone and moved to the big cities, forming a mass of refugees. Meanwhile, former SNOF fighters (who, being loyal to Tito, had been forced by EAM to leave Greece) set up a new pro-Yugoslav organization (NOF), returned to Greece and sided with the Greek Communists.
However, the 1948 Moscow-Belgrade breach, KKE's decision to side with Moscow and the subsequent cessation of Yugoslav aid to it, KKE's decision in January 1949 to support the formation of a "united Macedonia" within the context of a Balkan federation controlled by Moscow, in combination with political and military developments in Greece, brought about the defeat of the Communist forces.
After 1949, NOF fighters retreated into Yugoslavia; with them went that part of the Slavic-speaking population who did not share the Greek national identity.