The Domino Theory caused continued support for South Korea to a great extent. It was the cause in many different ways, both directly and indirectly, so much so that it was the main reason that the US was involved in the Korean War.
At the start of 1950, tensions in Korea were very high. At the end of WWII it had been split into two: the US occupied south and the Russian occupied north, with two different leaders for each zone. Both superpowers agreed at the Yalta Conference in 1945 that Korea would become independent in the next four years. This happened, but the USSR had put a lot of money into building up North Korea’s military in this time, while the US was more focussed on helping South Korea economically. This gave North Korea the perfect opportunity to attack in order to unite Korea under a single, communist government.
The Domino Theory was the key reason that the US was supporting South Korea. In order for containment to take place (an idea born out of the Domino Theory), the US had to continue support so as to prevent South Korea from falling to communism by being completely taken over by the North This by extension meant that the US’ support was preventing the Domino Theory.
The Domino Theory was also, by extent, a major reason why Truman chose to go ahead with sending troops into Korea. It was him who had put forward the Truman Doctrine which declared that it was the foreign policy of the United States to assist any country whose stability was threatened by communism. This put forward the idea of Containment, one that, since it had been suggested by Truman, the US public thought Truman would follow through with. However, when the Chinese Civil War re-started in 1946 Truman didn’t intervene at all to help the Chinese Nationalists against the Chinese Communists (later established as the People’s Republic of China in 1949 – to be known as PRC from this point on). This, in the eyes of the US public, was a sign of weakness from Truman, which...