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, with the Yellow Sea to the west and the Sea of Japan to the east. Like North Korea, South Korea claims to be the sole legitimate government of the entire peninsula and adjacent islands. It has a population of about 52 million, of which half live in the Seoul metropolitan 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 seventh century BC. From the mid first century BC, various polities consolidated into the rival kingdoms of Goguryeo, Baekje, and Silla. The lattermost eventually unified most of the peninsula for the first time in the late seventh century AD, while Balhae succeeded Goguryeo in the north. The Goryeo dynasty (918–1392) achieved lasting unification and established the basis for the modern Korean identity. The subsequent Joseon dynasty (1392–1897) generated cultural, economic, and scientific achievements and also established isolationism starting from the mid-17th century. The succeeding Korean Empire (1897–1910) sought modernization and reform but 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: the Soviet-occupied northern zone and the United States-occupied southern zone. 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.
