Papandreou's Center Union government enacted a number of farreaching social and political reforms. Prominent among them was the release of all political prisoners. To deal with the economic crises, Georgios Papandreou appointed his son Andreas, the former chairman of the Economics Department at the University of California at Berkeley, as minister of the economy. Many in the Center Union resented this move. Rising stars in the party such as Konstantinos Mitsotakis felt especially slighted by the appointment. The younger Papandreou, who held far more radical views than his father, soon became involved with a group of leftleaning military officers known as Aspida. The right viewed these developments suspiciously. Cabals formed in the army as once again rightist military men assumed the role of "protectors" of the nation. To regain control of the armed forces, Georgios Papandreou forced the resignation of his minister of defense and sought the king's approval to name himself minister of defense. The constitutional question again came to forefront when Constantine refused the request. In this case, the question was who controlled the military, the king or the prime minister, and the clash of personalities between the two men exacerbated the conflict.

Papandreou resigned in disgust in July 1965. In the succeeding months, a series of caretaker governments came and went, leaving the ship of state adrift. Constantine eventually called for elections in May 1967, and an overwhelming Center Union victory seemed certain. Fearing a purge of hard-line right-wingers from the military, a group of junior officers put Operation Prometheus into action in April 1967, and the government of Greece fell into the hands of the junta of the colonels.