Kim returned to Korea in September 1945 after the end of World War II and used both his guerrilla record and the support of Soviet occupation authorities to become the undisputed leader of North Korea. When North Korea was formally established on 9 September 1948, he became premier. The pro-Western Republic of Korea (ROK, South Korea) had already been established under the leadership of Syngman Rhee.
Kim possessed a burning ambition to reunite the Korean Peninsula under his rule. With Soviet and Chinese acquiescence and support, he launched a surprise military invasion across the 38th Parallel against South Korea on 25 June 1950. After initial success, however, the assault was repulsed by the forces of South Korea, the United States, and other nations under the flag of the United Nations (UN). Only the massive November 1950 Chinese intervention saved North Korea from defeat. The war eventually stalemated and ended with an uneasy cease-fire in 1953 that left the peninsula divided at the 38th Parallel. To this day, North and South Korea are still technically in a state of war, as no formal peace treaty has been signed.
In the aftermath of the Korean War, Kim systematically purged his political opponents, creating a highly regimented and centralized system that accorded him unlimited power and generated a formidable cult of personality. He was referred to by his subjects in North Korea as suryong, or "the Great Leader." Kim used Juche, or the ideology of self-reliance, to legitimize his regime and to keep foreign influences out of North Korea. Under his rule, North Korea became isolated from the world community and hard-pressed economically. Throughout much of the Cold War and beyond, North Korea remained one of the most enigmatic and closed societies in the world. In particular, after Kim's death in 1994, North Korea became increasingly unable to stabilize its sinking economy and to feed its own people.
Kim had made the United States his primary enemy, blaming Washington for the division of the peninsula in 1945. He also abhorred America for its 1950 intervention, which prevented reunification on his terms, and for turning South Korea into a virtual U.S. colony. Thus, he pursued a consistently hard-line policy toward the United States, as demonstrated by the USS Pueblo incident in 1968 and the brutal 1976 ax murders of two American officers in the demilitarized zone. On the other hand, Kim had long sought a dialogue with the United States in hopes of persuading the United States to withdraw its 37,000 troops from the peninsula. He also hoped that a closer relationship with Washington would offset the collapse of the North Korean–Soviet alliance and the weakening of North Korea's relations with Beijing. After March 1993, Pyongyang began using its nuclear weapons program as a bargaining chip for recognition, security assurances, and economic aid from the United States and other Western nations. For a failing and isolated regime with few other cards to play, this potentially deadly brinkmanship proved moderately successful. In 1994, the United States promised North Korea modest aid and help building nuclear power plants that could not be used to produce weapons-grade uranium. In return, the North Koreans were to abandon their nuclear weapons programs, a pledge that they evidently had no intention of fulfilling.
Kim died of a massive heart attack on 8 July 1994 in Pyongyang, just before what would have been a historic South Korean–North Korean summit with South Korean President Kim Young Sam. Kim's son, Kim Jong Il, succeeded his father as absolute ruler of North Korea. Kim Il Sung is as omnipresent in death as in life, and the junior Kim has ruled North Korea in accordance with the teachings of the departed Great Leader.
For the past half century, while Pyongyang has glorified Kim as something akin to a deity, Seoul has portrayed him as a demon, a scoundrel, and a fraud. But South Korean President Kim Dae Jung's tenacious efforts to engage Pyongyang have helped to erode such Cold War–era attitudes in South Korea. As an example, some lines in a newly approved high school textbook in South Korea for the first time credited Kim Il Sung for his role in combating Japanese colonialism. The passages symbolize rapidly changing South Korean views of North Korea.
Oberdorfer, Don. The Two Koreas: A Contemporary History. Revised and updated ed. New York: Basic Books, 2002.; Suh, Dae-Sook. Kim Il Sung: The North Korean Leader. New York: Columbia University Press, 1988.