After defeating Japan in World War II, Soviet forces occupied the Korean Peninsula north of the 38th parallel and U.S. forces occupied the south. Korea was intended to be reunited eventually, but the Soviets established a communist regime in their zone, while in 1947 the United Nations assumed control of the U.S. zone and sought to foster a democratic pan-Korean state. Amid partisan warfare in the south, the Republic of Korea was established in 1948. By 1950 the violence had convinced North Korean leader Kim Il-Sung that a war under Soviet auspices was necessary for reunification.