In 1972, the Fourth Republic was established following a constitutional referendum that approved the Yushin Constitution, which provided de facto dictatorial powers to President Park Chung-hee. Under Park and his Democratic Republican Party, the country entered into an authoritarian period known as the Yushin System. Following Park's assassination in 1979, Choi Kyu-hah took over as president but martial law was declared and the country fell into political instability. Chun Doo-hwan then overthrew Choi and launched a coup d'état in December 1979. He then suppressed the Gwangju Democratization Movement against martial law in May 1980, after which he dissolved the National Assembly and was elected president of the National Council for Reunification. The Fourth republic was then dissolved when a new constitution was adopted in March 1981 and replaced with the Fifth Republic of Korea.