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.
Syngman Rhee
On July 20, 1948, Rhee was elected president of the Republic of Korea in the South Korean presidential election, 1948 with 92.3% of the vote; the second candidate, Kim Gu, received 6.7% of the vote. On August 15, the Republic of Korea was formally established in South Korea and Rhee was inaugurated as the first President of the Republic of Korea. The next month, on September 9, the north also proclaimed statehood as the Democratic People's Republic of Korea. Rhee himself had been an independence activist, and his relations with the "chinilpa" Korean elites who had collaborated with the Japanese were, in the words of the South Korean historian Kyung Moon Hwang, often "contentious," but in the end an understanding was reached in which, in exchange for their support, Rhee would not purge the elites. In particular, the Koreans who had served in the colonial-era National Police, whom the Americans had retained after August 1945, were promised by Rhee that their jobs would not be threatened by him. Upon independence in 1948, 53% of South Korean police officers were men who had served in the National Police during the Japanese occupation.