On September 9, 1948, the Democratic People's Republic of Korea was proclaimed in Pyongyang, with Kim Il Sung as premier. It came three weeks after the Republic of Korea had been declared in Seoul on August 15, 1948, under Syngman Rhee. Both governments claimed to represent all of Korea, and neither recognized the other.
Korea had been under Japanese rule since 1910 and was freed in August 1945 by a decision taken elsewhere. The United States and the Soviet Union, both about to have troops in the country for the first time, agreed to divide the occupation at the 38th parallel to take the Japanese surrender, with the Soviets north of it and the Americans south. Two American officers drew it in a hurry, from a National Geographic map, on the night of August 10, 1945. No Korean was consulted.
It was meant to be temporary. The Moscow conference of foreign ministers in December 1945 proposed a four-power trusteeship of up to five years and a joint commission to form a single government, and the commission met and got nowhere through 1946 and 1947 as the two sides disagreed about who could be consulted and what a provisional government would look like. In September 1947 Washington took the question to the United Nations, which called for elections across the peninsula. The Soviet command refused to allow UN observers north of the parallel, and elections were held in the south only, in May 1948. The north answered with its own.
Kim Il Sung was 33. He had spent the war years in the Soviet Far East, ending as a major in the Red Army, and he was chosen by the Soviet authorities over other Korean candidates, some of whom had stronger credentials inside the country. His government moved quickly: land reform in 1946, nationalization of industry, and the creation of the Korean People's Army, with Soviet equipment and Soviet-trained officers returned from China and the USSR.
Kim wanted to unify the peninsula by force. He needed Moscow's agreement. He got it in 1950. North Korean forces crossed the 38th parallel on June 25, 1950, which began the Korean War. The armistice of July 27, 1953 left the border close to where it had been drawn in 1945, and the demilitarized zone that replaced it is the last heavily fortified frontier of the Cold War. September 9 is still the country's national day.