The Fourth Republic was founded on the approval of the Yushin Constitution in the 1972 constitutional referendum, codifying the "de facto" dictatorial powers held by President Park Chung-hee, and succeeding the Third Republic. Park and his Democratic Republican Party ruled under the centralized and authoritarian Yushin System until the assassination of Park on 26 October 1979. The Fourth Republic entered a period of political instability under Park's successor, Choi Kyu-hah, and the escalating martial law declared after Park's death. Choi was unofficially overthrown by Chun Doo-hwan in the coup d'état of December Twelfth in December 1979, and began the armed suppression of the Gwangju Democratization Movement against martial law. Chun launched the coup d'état of May Seventeenth in May 1980, establishing a military dictatorship under the National Council for Reunification and dissolving the National Assembly, and was elected President by the council in the August 1980 presidential election. The Fourth Republic was dissolved on the adoption of a new constitution in March 1981 and replaced with the Fifth Republic of Korea.