Causes of the Korean War

Before WW2, Korea was ruled by Japan but this had to change when Japan was defeated during the war. Troops in the North surrendered to the Soviet forces and troops in the South surrendered to the US forces creating a temporary split along the 38th parallel. However, this temporary split lasted longer than expected as the Soviets allowed Kim Il Sung, a communist, to rule the North and after an election, Syngman Rhee, a capitalist, was issued to rule the South. The opposing ideologies created tension of a wanted unified Korea. 

The Truman Doctrine was announced in March 1947 by US President Harry Truman. He said that the USA would come to the aid, with money and miliatry help, of any country under the threat of communism. Their main aim was to 'contain communsim'. When China became communist in 1949, this worried the USA as they were frightened that this spread of communism may find its way into Korea. 

Both Kim Il Sung and Syngman Rhee were Korean nationalists meaning that they wanted a united independent Korea. However this was very challenging as both leaders had opposing ideologies and were fighting for each one to win. This caused a lot of tension and eventually lead to Kim Il Sung's invasion into South Korea. 

When China became a communist country, the Security Council had a meeting to discuss whether they were to all the new Chinese government to be a part. However, the USA unsurprisingly vetoed this decision resulting in the USSR storming out and refusing to be present in any other Security Council meetings in the future. This proved well for the future, as when North Korea invaded the South, the US forces were allowed to get involved due to the USSR's absence in the UN. 

On the 25th June 1950, Kim Il Sung decided to invade the South of Korea with support of Stalin and China. This gave Kim Il Sung confidence as he had support and people behind him who would surely unite Korea. This invasion was the initial trigger fsctor of the start of the Korean War.