History of South Korea
On August 15, 1948, the Republic of Korea was formally established, with Rhee Syngman as the first president. With the establishment of Rhee's government, de jure sovereignty also passed into the new government. On September 9, 1948, a communist regime, the Democratic People's Republic of Korea (North Korea), was proclaimed under Kim Il-sung. However, on December 12, 1948, by its resolution 195 in the Third General Assembly, the United Nations recognized the Republic of Korea as the sole legal government of Korea.
United Nations Security Council Resolution 82
At the end of World War II, the Korean Peninsula, which up to that point had been occupied by the Empire of Japan, was divided along the 38th Parallel. To the north, the Soviet Union (USSR) occupied the country, which established itself as a communist state, the Democratic People's Republic of Korea under Kim Il Sung. To the south, the United States (US) occupied the country, establishing the Republic of Korea under an autocratic anti-communist leader, Syngman Rhee. As tensions rose between the US and the USSR, each government in Korea claimed it had sovereignty over the whole country.