A series of democratic movements in South Korea began with the assassination of President Park Chung-hee on October 26, 1979. The abrupt termination of Park's 18-year authoritarian rule left a power vacuum and led to political and social instability. While President Choi Kyu-hah, the successor to the Presidency after Park's death, had no dominant control over the government, South Korean Army major general Chun Doo-hwan, the chief of the Defense Security Command, seized military power through the Coup d'état of December Twelfth and tried to intervene in domestic issues. The military however could not explicitly reveal its political ambitions and had no obvious influence over the civil administration before the mass civil unrest in May 1980.