"The borders between Greece and Serbia were defined in 1913 on the basis of the advances of the armies of the two nations during the first Balkan war. The border between Greece and Bulgaria was defined at the Treaty of Bucharest. Since then, the borders of the three nations had remained the same. Macedonia, a region mostly of Greece since ancient times, was divided into three perhaps even four parts, with Greece keeping the largest portion of about 50%, then-Yugoslavia receiving about 35%, Bulgaria about 10% and a small percentage eventually ending in Albania. The Greek people on the portion of the Macedonia part in Greece have been there since time immemorial -- over more than forty centuries before the Slavs arrived. The language spoken in the Greek region since antiquity is Greek, whereas the language of the former-Yugoslavia portion is a Slavic dialect of Bulgarian (Marline Simons, The New York Times, February 3, 1992). As a matter of fact, the portion of Macedonia in then-Yugoslavia was part of the Eastern Branch of the Roman Empire. The people who ruled over Serbia spoke Greek. Constantinople was their headquarters. Their main trade was to the South and East..."
January 1, 1970
https://en.wikiquote.org/wiki/Macedonia_(Greece)