<p>This article aims to examine the links between the fall of Détente and the dysfunction of the U.S. - Japan alliance in the end of 1970s.</p><p>The previous studies have explained that Secretary of State Vance who sought for keeping Détente with the Soviet Union and Presidential Assistant Brzezinski who sought for anti-Soviet coalition with China were confronted each other in Carter Administration, and the administration abandoned the Détente policies such as SALT II after President Carter decided to support for Brzezinski.</p><p>How did Japan commit with the process of the fall of Détente? The American researchers have tended to insist that Japan was a junior partner of the U.S. and China during the process. But the Japanese researchers have verified that Fukuda and Ohira Administration managed to keep independence from the anti-Soviet coalition of the U.S. and China, because Japan managed to stabilize the regional order of Asia, especially Indochina. They have also pointed out that the outbreak of the New Cold War caused by Soviet’s invasion of Afghanistan constrained Japan’s diplomatic independence than before. However, all the previous studies have never discussed how the split in Carter Administration affected Japanese diplomacy.</p><p>In this article, I address the question of how the division in Carter Administration and the dysfunction of the U.S. - Japan alliance linked, to point out that the interaction prevented Japan from continuing her own diplomacy strategy for Vietnam, a main part of effort to keep Détente during the period of Ohira Administration.</p><p>In conclusion, I would like to indicate three points, the feature of Ohira’s strategy for keeping Détente, the way Carter Administration interrupted Japan’s own diplomacy, and the point of no return to the fall of the Détente. Firstly, Ohira Administration pursued that Japan would be a balancer in Asia by taking advantage of economic assistance to ease of tension between the Soviet Union and China, China and Vietnam, or Vietnam and ASEAN countries. Secondly, Carter Administration didn’t give no clear guideline about their policy toward the Soviet Union and China to Japan because of their internal split. In addition, Carter Administration was indifferent to how their diplomacy influenced that of Japan. What is worse, Carter Administration deprived Japan of her diplomatic leverage because the Administration lacked the power to influence China and Vietnam. Thirdly, the U.S. - China normalization announced in December 1978 was the point of no return to the fall of the Détente.</p>