Since 1978, The United States and Japan had ‘Guidelines for Japan-U.S. Defense Cooperation’. The 1978 Guidelines focusedon Japan’s sel-defense. The collapsed of Soviet Union made strong the U.S.-Japan relationship. The 1978 Guidelines was revised in 1997. The United States decided to create ‘The New Guidelines for the Japan-U.S. Defense Cooperation’ in 2015 because the United States wanted to strengthen alliance prepare Japan with increased Japan’s arms defense to balance of power the rise of China and development nuclear and missile North Korea, and cut the cost of the U.S. defense development. The main purpose of this study was to find out and describe the reasons of the United States decide to create ‘The New Guidelines for the Japan-U.S. Defense Cooperation’ in 2015. This research was casual explanation research. It explained the cause of phenomenon which will be observed. The research method used the qualitative method which used the content analysis toward some books, e-journal, document, and news.