One facet of the changing attitude toward Korea and whether to get involved was <answer>Japan</answer>. Especially after the fall of China to the Communists, U.S. East Asian experts saw <answer>Japan</answer> 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 <answer>Japan</answer> increased the importance of South Korea. Said Kim: "The recognition that the security of <answer>Japan</answer> 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 <answer>Japan</answer>."
What country was believed to provide a counterbalance to China's and the Soviet Union's involvement in Korea?
Japan