Formerly a single nation that was annexed by Japan in 1910, the Korean Peninsula has been divided into North Korea and South Korea since the end of World War II on 2 September 1945. The two governments were founded in the two regions in 1948, leading to the consolidation of division. The two countries became opposite and engaged in the Korean War from 1950 to 1953 which ended in an armistice agreement but without a peace treaty. North Korea is a one-party totalitarian state run by the Kim dynasty. South Korea was formerly governed by a succession of military dictatorships, save for a brief one-year democratic period from 1960 to 1961, until thorough democratization in 1987, after which direct elections were held. Both nations claim the entire Korean peninsula and outlying islands. Both nations joined the United Nations in 1991 and are recognized by most member states. Since the 1970s, both nations have held informal diplomatic dialogues in order to ease military tensions. In 2000, President Kim Dae-jung became the first President of South Korea to visit North Korea, 55 years after the peninsula was divided.

Under President Kim, South Korea adopted the Sunshine Policy in pursuit of more peaceful relationships with North Korea. The policy established the Kaesong Industrial Region, among other things. This policy was continued by the next president Roh Moo-hyun who also visited North Korea in 2007 and met with North Korean leader Kim Jong-il. Through this meeting both leaders signed a declaration to pursue peace and recover inter-Korean relations. However, faced with growing criticism, the Sunshine Policy was discontinued under the next two governments. During Lee Myung-bak and Park Geun-Hye's presidencies, the relationship between North and South Korea became more hostile.

In 2018, beginning with North Korea's participation in the 2018 Winter Olympics, the relationship has seen a major diplomatic breakthrough and become significantly warmer. In April 2018, the two countries signed the Panmunjom Declaration for Peace, Prosperity and Unification of the Korean Peninsula. In 2018, a majority of South Koreans approved the new relationship. The summits between North and South Korea have also facilitated positive relationships between North Korea and the United States. However, tensions between the two countries remain.