Truman wanting to appear tough in the face of communism, and to avoid direct contact with the USSR. The US also wanted to protect Japan as their security was vital.
However there are still reasons on why US involvement wasn't a success. these reasons being the change of objective as the US now wanted to ‘roll back’, Truman looking weak and ineffective and also the way China was dealt with during the conflict.
Domestic issues was another very important reason on how the US involvement had also failed as people were losing faith in the war and opinions changed quickly, the war was also very costly which meant money that should of been spent at home, and money that could of gone towards helping the civil rights movement went towards the war. This allowed the war to become very unpopular with the American citizens. One of the most significant ways in which US involvement in the Korean conflict could be judged as a success is the fact that the US had got involved in the conflict to protect the independence of South Korea. This was very important as without the support of the
United States, South Korea would of been overrun within the first phase of the war. This was down to economic costs and the vast number of men that North Korea and their allies would of had on their front line invading the south. This was a great success of US involvement as they successfully helped South Korea regain control and push the North out. As well as protecting the independence of South Korea, the USA also got involved to
‘contain’ communism. The United States managed to keep South Korea noncommunist after creating the halt line at the 38th parallel.