Throughout 2021, the security environment in northeast Asia became more challenging. The United States and its allies deployed the largest number of troops in the Western Pacific since the end of the Cold War, while the international community increasingly called for China to maintain peace and stability in the Taiwan Strait as it increased military pressure on Taiwan. Despite its economic difficulties, North Korea pushed ahead with the enhancement of its nuclear capabilities to make their nuclear weapon possession a fait accompli and the modernization of its armed forces in order to rebuild its relations with the United States. Meanwhile, the challenges facing the cooperative systems among the United States, Republic of Korea (ROK) and Japan were highlighted. As the security environment surrounding Japan has become increasingly severe, there was intensive discussion in Japan about Japan's role in the event of a contingency in Taiwan, and about attacking enemy bases in preparation for the threat of North Korean and Chinese new nuclear and missile capabilities.