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.
North Korea–Russia relations
Diplomatic relations between North Korea (Democratic People's Republic of Korea, DPRK) and the Soviet Union (Union of Soviet Socialist Republics, USSR, the predecessor state to the Russian Federation) were first established on October 12, 1948 shortly after the Democratic People's Republic of Korea was proclaimed. During the Korean War, the Korean People's Army was supported by the Soviet military forces. North Korea was founded as part of the Communist bloc, and received major Russian support. China and the Soviet Union competed for influence in North Korea during the Sino-Soviet split in the 1960s, as the North Korea tried to maintain good relations with both countries.