The Korean War was a war between North Korea and South Korea. The war began on 25 June 1950 when North Korea invaded South Korea.
At the end of World War II, the Soviet Union and the United States liberated Korea from imperial Japanese colonial control on 15 August 1945. After the war had ended, 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. With the border set at the 38th parallel in 1948, two sovereign states were established as a result of geopolitical tensions of the Cold War. A socialist state was established in the north under the communist leadership of Kim Il-sung and a capitalist state in the south under the anti-communist 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.
The conflict escalated into warfare when North Korean military forces—supported by the Soviet Union and China—crossed the border and advanced into South Korea on 25 June 1950.