Truman’s decision to become involved in the Korean conflict is an example of the US policy of

Containment

the next one is: prevent communism spreading to the U. S

Explanation:

correct on edge

The Correct answer is the doctrine of Containment. Indeed, Stalin's Soviet Union had engaged in a series o Geo-political moves to assert and/or increase its influence and spread Stalinist-styled Communism in Eastern Europe, Asia, the Caribbean, Africa and the Americas.

Truman wanted to politically and economically weaken the Soviet Union by keeping it from expanding its influence and sociopolitical model worldwide. His first move was to provide $400 US million to combat Communism in Greece and Turkey where their popularity kept spreading. Then there was the proxy war of Korea where a US-led coalition fought Soviet-led forces including hundreds of thousands of Chinese "volunteers".

Part of the strategy was also to engage in an arm's race with the Soviet Union that included the manufacture of thousands of nuclear weapons. However, one of the major paradoxes of the Cold War was the extensive development of nuclear weapons and the reluctance to actually use them in order to avoid mutually assured destruction.