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.
South Korea–Taiwan relations
The People's Republic of China (PRC) was founded in 1949 following the Chinese Civil War and Republic of Korea maintained relations with the Republic of China (ROC), whose government relocated to Taiwan. The United Nations condemned North Korea's military aggression against Republic of Korea in United Nations Security Council Resolution 82 and United Nations Security Council Resolution 84. The ROC voted in favor of both United Nations resolutions. During the Korean War, the ROC supplied material aid to ROK, while the People's Republic of China gave North Korea combatants to support the People's Volunteer Army.