Weeks after the US-backed Republic of Korea was established in the south, Kim Il Sung proclaimed the Democratic People's Republic of Korea in Pyongyang, with Soviet backing. The declaration hardened the division of a peninsula that had been unified for over a millennium, setting the stage for the Korean War less than two years later.
The Korean peninsula, liberated from 35 years of brutal Japanese colonial rule in 1945, was carved into occupation zones almost as an afterthought—American forces below the 38th parallel, Soviet forces above it. What was meant to be temporary hardened quickly into permanent division as Cold War tensions calcified.
When the Republic of Korea was established in Seoul on August 15, 1948, under Syngman Rhee, the Soviet-backed authorities in the north responded by formalizing their own state. On September 9, Kim Il Sung, a former guerrilla fighter against Japanese occupation who had spent years in the Soviet Union, declared the founding of the Democratic People's Republic of Korea.
Both governments claimed sovereignty over the entire peninsula, a rivalry that would erupt into open war in June 1950 when North Korean forces invaded the south. That war would kill an estimated 2.5 million people and end in an armistice, not a peace treaty—leaving the peninsula still technically at war and the two Koreas among the most starkly divided nations on Earth, a division that endures more than seven decades later.