This Study aims to find out the reason of protectionism policy of the United States under Trumps administration able to impacts to Japan. In the protectionism that Trump did there are several actions conducted such as withdrawal from TPP (Trans-Pacific Partnership), a limiting the number of immigrants that entering in the United States and applying Border Tax that taxes on imported products from other countries in order to protect similar product made by local companies. United States-Japan alliance established for a long time. In which both parties depend on each other. Japan depends on the military and economic aspects of the United States and United States is one of the trading partners of Japan in which many goods from Japan enter the United States. In order explain the relation between United States and Japan, this researcher uses the interdependency to prove the relation on military and economy between two parties. Methodology applied in this research is qualitative method by collecting data from various sources such as book, journal and website. The result of this research show the intertwined between US and Japan in military and economy sector