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
The history of Korea begins with the founding of Joseon (also known as "Gojoseon", or Old Joseon, to differentiate it with the 14th century dynasty) in 2333 BCE by Dangun, according to Korea's foundation mythology. Gojoseon expanded until it controlled the northern Korean Peninsula and parts of Manchuria. Gija Joseon was purportedly founded in the 12th century BC, but its existence and role have been controversial in the modern era. In 108 BCE, the Han dynasty defeated Wiman Joseon and installed four commanderies in the northern Korean peninsula. Three of the commanderies fell or retreated westward within a few decades. As Lelang commandery was destroyed and rebuilt around this time, the place gradually moved toward Liaodong. Thus, its force was diminished and it only served as a trade center until it was conquered by Goguryeo in 313.