Park returned to southern Korea in May 1946 and became an officer in the Constabulary Army during the U.S. occupation of Korea. The newly established South Korean government, under the leadership of Syngman Rhee, arrested Park in November 1948 on charges that he led a communist cell in the Constabulary Army. Park was subsequently sentenced to death by a military court, but his sentence was commuted by Rhee at the urging of several high-ranking Korean military officers.
On 30 June 1950, immediately after the Korean War began, Park returned to active service as a major. He was promoted to lieutenant colonel that September and to colonel in April 1951. As a colonel, he became the artillery commander of II Corps in February 1953 and of III Corps in May 1953. Advanced to brigadier general in November 1953, he became commander of the 5th Division in July 1955 and of the 7th Division in September 1957. Promoted to major general in March 1958, that June he became chief of staff of the First Army. In July 1959 he headed the 6th District Command, which had responsibility for the defense of Seoul. He then commanded in succession the Quartermaster Base and the 1st District Command. In September 1960 he became chief of the Operations Staff of the South Korean Army and, that September, deputy commander of the Second Army.
In April 1960, mass antigovernment demonstrations forced the aging Rhee from power. That July, national elections brought a coalition government to power with Yun Po Sun as president and Chang Myon (John W. Chang) as premier. Despite their attempts to initiate needed reforms, their efforts largely failed, and antigovernment violence increased. Taking advantage of the situation, a group of young officers helped Park seize power in a military coup on 16 May 1961.
Park was promoted to lieutenant general in August 1961 and to general in November 1961. Following the coup, he was consecutively elected president in 1963, 1967, 1971, 1972, and 1978. Initially, he embarked on a generally successful economic modernization program that brought stability and increased prosperity to his country. During 1965–1973, he dispatched more than 47,000 South Korean troops to Vietnam at the request of the United States. From the early 1970s, however, public resistance against his authoritarian regime increased. The once-flourishing South Korean economy was on the skids by the mid-1970s. Park's iron-fisted rule ended abruptly when he was assassinated in Seoul by his director of the Korean Central Intelligence Agency, Kim Chae Gyu, on 26 October 1979.
Cumings, Bruce. Korea's Place in the Sun: A Modern History. New York: Norton, 1997.; Oberdorfer, Don. The Two Koreas: A Contemporary History. Revised and updated ed. New York: Basic Books, 2002.