Final answer:
American involvement in Korea was more direct due to the division of Korea post-WWII, the US's responsibility for the government in South Korea, the containment policy, and domestic issues that led to increased defense spending.
Step-by-step explanation:
Reasons for Intense American Involvement in the Korean War
The United States' involvement in Korea was more direct and intense than in China's civil war for several reasons. Firstly, Korea had been divided post-World War II into two regions, with the North controlled by the Soviets and the South by the Americans. When North Korea, backed by the Soviet Union, invaded South Korea in an attempt to unify the peninsula under Communist rule, the United States, concerned with containment of communism and maintaining its credibility, led a United Nations military response. The Domino Theory was also at play, with fears that a Communist victory in Korea could spread throughout Asia.
Secondly, Korea's situation presented a direct challenge to the United States which had established the government in South Korea. South Korea was seen as a test of the US's commitment to fighting communism globally. Furthermore, the Korean Conflict occurred just after the Communist takeover of China, which compounded the fear of Communist expansion.
Lastly, domestic issues in the United States also played a role. The outbreak of the war justified increased defense spending as recommended in NSC-68, reflecting a shift in American foreign policy.