After the 1944-49 Greek civil war, the country became a member of NATO. In 1952 Greece was governed by the Greek Rally of Marshal Alexandros Papagos and its successor, the National Radical Union (ERE) of Constantine Karamanlis. In 1963, the Center Union Party of George Papandreou was elected and governed until July 1965.

A succession of unstable coalition governments followed. Following a 1974 referendum, parliament elected Constantine Tsatsos as President of the republic. In the parliamentary elections of 1977, New Democracy again won a majority of seats. In May 1980, Prime Minister Karamanlis was elected to succeed Tsatsos as president.

In parliamentary elections held on October 18, 1981, Greece elected its first socialist government led by Andreas Papandreou. In 1996, following a protracted illness, Prime Minister Papandreou resigned and was replaced as Prime Minister by former Minister of Industry Constantine Simitis.