WWII helped to create the Korean War by creating the split between North Korea and South Korea.
At the very end of WWII, the Soviet Union finally agreed to get into the war against Japan. The US had been pushing for this, but the Soviets were reluctant. They got into the war on August 9, 1945, three days after the first atomic bomb was dropped on Hiroshima. The Soviets attacked Japanese forces in Manchuria and then later moved into the northern part of Korea. They were given control of that part of the country after the war. There were supposed to be elections, but this did not happen and there came to be two Koreas, each claiming to be the legitimate government for the whole country.
It was this split that caused the Korean War. In June of 1950, North Korea invaded the South in an attempt to reunify the peninsula. This was the start of the Korean War.