South Korea–United States relations
Following Japanese surrender at the end of the Second World War, the Allied Powers divided the Korean peninsula along the 38th Parallel with two occupation zones with the United States in the south, and the Soviet Union in the north that would later become North Korea. On August 15, 1948, the southern half of Korea declared independence as the Republic of Korea with Syngman Rhee as president. The United States recognized the Republic of Korea as an independent state on January 1, 1949 and diplomatic relations between two countries were established on March 25 in the following year.
Cross-border skirmishes and raids at the 38th Parallel escalated into open warfare when the North Korean forces invaded South Korea on June 25, 1950. The Korean War broke out when North Korea invaded South Korea. In response, 16 member countries of the United Nations, including the United States, came to the defense of South Korea. It was the first significant armed conflict of the Cold War with extensive deployment of American and other troops.
May 16 coup
After rigged elections in March 1960, growing protests developed into the April Revolution, and Rhee was pressured by the United States into a peaceful resignation on April 26. With Rhee out of the way, a new constitution was promulgated establishing the Second Republic, and legislative elections on June 29 resulted in a landslide victory for the Democratic Party, with Rhee's Liberals reduced to a mere two seats in the newly constituted lower house of the National Assembly. The Democrat Yun Bo-seon was elected as figurehead president in August, and Chang Myon, former Vice-President, took over as Prime Minister with executive authority under the parliamentary republican system established by the new constitution.
The Second Republic was beset with problems from the start, with bitter factionalism in the ruling Democratic Party competing with implacable popular unrest for the government's attention. The South Korean economy deteriorated under heavy inflation and high rates of unemployment, while recorded crime rates more than doubled; from December 1960 to April 1961, for example, the price of rice increased by 60 percent, while unemployment remained above 23%. Widespread food shortages resulted. Chang Myon, meanwhile, representing the Democratic Party's "New Faction", had been elected Prime Minister by the thin margin of three votes. Purges of Rhee's appointees were rendered ineffective in the public eye by Chang's manipulation of the suspect list to favour wealthy businessmen and powerful generals. Although Rhee had been removed and a democratic constitution instituted, the "liberation aristocrats" remained in power, and the worsening problems facing South Korea were proving insurmountable for the new government.