One facet of the changing attitude toward Korea and whether to get involved was Japan. Especially after the fall of China to the Communists, U.S. East Asian experts saw Japan as the critical counterweight to the Soviet Union and China in the region. While there was no United States policy that dealt with South Korea directly as a national interest, its proximity to Japan increased the importance of South Korea. Said Kim: "The recognition that the security of Japan required a non-hostile Korea led directly to President Truman's decision to intervene... The essential point... is that the American response to the North Korean attack stemmed from considerations of US policy toward Japan."

What country was believed to provide a counterbalance to China's and the Soviet Union's involvement in Korea?