This study explores the evolution of Greek-Romanian diplomatic relations from 1933 to 1948, a period marked by regional instability, shifting alliances, and minority issues. Despite early cooperation through inter-Balkan initiatives and economic agreements, tensions arose over the Aromanian (Vlach) minority in Greece. The authoritarian regimes of Metaxas in Greece and Carol II in Romania deepened political and ethnic divisions. During WWII, Romania’s alliance with the Axis and Greece’s occupation strained ties further, with arrests and deportations of romanised Vlachs heightening diplomatic rifts. Post-war efforts to restore relations failed amid the Cold War’s onset, culminating in Romania’s protest against Greece’s treatment of its Vlach minority. The article highlights the fragility of regional alliances under nationalist and totalitarian, pressures.