The division of Korea between North and South Korea was the result of the Allied victory in World War II in 1945, ending the Empire of Japan's 35-year colonial rule of Korea by General Order No. 1. The United States and the Soviet Unionagreed to temporarily occupy the country with the zone of control along the 38th parallel.
With the onset of the Cold War, negotiations between the United States and the Soviet Union failed to lead to an independent, unified Korea. In 1948, UN-supervised elections were held in the US-occupied south only. This led to the establishment of the Republic of Korea in South Korea, which was promptly followed by the establishment of the Democratic People's Republic of Korea in North Korea. The United States supported the South, and the Soviet Union supported the North, and each government claimed sovereignty over the whole Korean peninsula.
The Korean War (1950–53) left the two Koreas separated by the Korean Demilitarized Zone in the later part of the Cold War and beyond. The 21st century saw some improved relations between the two sides, overseen in the South by liberal governments, who were more amicable towards the North than previous governments had been. These changes were largely reversed under conservative South Korean president Lee Myung-bak who opposed the North's continued development of nuclear weapons.