In 1910, Japan put Korea under Japanese rule and was still ruling Korea when World War Two ended. When Japan surrendered, the United States and the USSR agreed to split Korea into two temporary occupation zones with USSR occupying the North and USA occupying the South Relations between the two occupying powers were bad and when China became Communist in October 1949, the President of the USA, Harry Truman, was very worried that other countries around China may also become Communist, such as Japan and that's where the containment strategy began to be used