The Korean War was a war between North Korea, with military support from China and the Soviet Union, and South Korea, backed by personnel from the United Nations. The war began on 25 June 1950 when North Korea invaded South Korea following clashes along the border and insurrections in the south. The war ended unofficially on 27 July 1953 in an armistice.
After the surrender of Japan at the end of World War II, on 15 August 1945, Korea was divided at the 38th parallel into two zones of occupation. The Soviets administered the northern-half and the Americans administered the southern-half. In 1948, as a result of Cold War tensions, the occupation zones became two sovereign states. A socialist state was established in the north under the totalitarian leadership of Kim Il-sung and a capitalist state in the south under the authoritarian leadership of Syngman Rhee. Both governments of the two new Korean states claimed to be the sole legitimate government of all of Korea, and neither accepted the border as permanent.
North Korean Korean People's Army forces crossed the border and drove into South Korea on 25 June 1950.