Japan is prohibited from entering into external conflicts under the US-Japan Status of Forces Agreement of 1954. They are limited to the Japanese Self-Defense Forces. The US is bound to defend Japan under this agreement.
Unified military forces of Japan
The Japan Self-Defense Forces are the military forces of Japan. Established in 1954, the JSDF comprises the Japan Ground Self-Defense Force, the Japan Maritime Self-Defense Force, and the Japan Air Self-Defense Force. They are controlled by the Ministry of Defense with the Prime Minister as commander-in-chief. Since the end of the Cold War, and particularly into the 21st century, increased tensions with North Korea, China, and Russia have reignited debate over the status of the JSDF and their relationship to Japanese society.
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