Since Donald Trump took office，he has adhered to the guideline of “America first” as his foreign policy，and the alliance with South Korea and Japan has been shaken and cracked. There are growing differences between the United States and the two major allies in East Asian on issues such as sharing defense costs and free trade agreements. What’s more，in the face of the protracted and increasingly intensified friction between South Korea and Japan，the Trump administration was unable to carry out effective alliance management，resulting in damage to the trilateral relationship. With the outbreak of the COVID-19 epidemic，the Trump administration has accelerated the containment of China，especially in the implementation of the Indo-Pacific Strategy. For this reason，the United States has continuously required South Korea and Japan to participate in the Indo-Pacific Strategy and join all mechanisms to contain China，forcing them to choose sides，which temporarily caused South Korea and Japan to fall into a dilemma. Since Biden took office in 2021，he vowed to repair the alliance relationship and prioritize the reshaping of the East Asian alliance. The US-South Korea alliance and the US-Japan alliance is being repaired，but this alliance system in the East Asia is also facing enormous challenges with the development of the East Asian situation.