South Korea, officially the Republic of Korea (ROK), is a country in East Asia. It constitutes the southern half of the Korean Peninsula and borders North Korea along the Korean Demilitarized Zone. The country’s western border is formed by the Yellow Sea, while its eastern border is defined by the Sea of Japan. Like North Korea, South Korea claims to be the sole legitimate government of the entire peninsula and adjacent islands. It has a population of 51.96 million, of which half live in the Seoul Capital Area, the ninth most populous metropolitan area in the world. Other major cities include Busan, Daegu, and Incheon.
The Korean Peninsula was inhabited as early as the Lower Paleolithic period. Its first kingdom was noted in Chinese records in the early 7th century BCE. After the unification of the Three Kingdoms of Korea into Silla and Balhae in the late 7th century, Korea was ruled by the Goryeo dynasty (918–1392) and the Joseon dynasty (1392–1897). The succeeding Korean Empire (1897–1910) was annexed in 1910 into the Empire of Japan. Japanese rule ended following Japan’s surrender in World War II, after which Korea was divided into two zones: a northern zone, which was occupied by the Soviet Union, and a southern zone, which was occupied by the United States. After negotiations on reunification failed, the southern zone became the Republic of Korea in August 1948, while the northern zone became the communist Democratic People’s Republic of Korea the following month.
In 1950, a North Korean invasion began the Korean War, which ended in 1953 after extensive fighting involving the American-led United Nations Command and the People’s Volunteer Army from China with Soviet assistance. The war left 3 million Koreans dead and the economy in ruins. The authoritarian First Republic of Korea led by Syngman Rhee was overthrown in the April Revolution of 1960. However, the Second Republic failed to control the