Korean Peninsula crisis has been occuring since 1950s. Until now, the crisis of the two Koreas keep going as the North keeps doing any efforts that leads to escalate the conflict. The targets of their nuclear weapon are the United States (U.S.) and their allies which are South Korea and Japan. In 2017, U.S. initiated trilateral military alliance with its allies which aims at countering North Korea’s nuclear and missile provocation. But surprisingly, South Korea stated that they do not want to join trilateral military alliance with U.S. and Japan. South Korea’s domestic politic condition and pressure from China regarding this issue are probably the reasons why South Korea chose to refuse to join the alliance.