South Korea, officially the Republic of Korea (ROK), is a country in East Asia. It constitutes the southern part 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. 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 roughly half live in the Seoul Capital Area, the fourth most populous metropolitan area in the world. Other major cities include Incheon, Busan, and Daegu.

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. Following 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 occupied by the Soviet Union, and a southern zone 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.