@sincity ,
I will reiterate , again, that Japan and the United States are strategic partners, and time honored allies. The United States' military defense of Japan as explicitly stated in our Mutual Defense Treaty -- that both Japan and the United States will come to the aid of each other in case of military attack and provocation. Our collective effort together in the Cold War enabled us to take care of any Soviet exigencies. This framework remains to this day. ]
US occupied Japan since end of WW2, the Japan Pacifist Constitution was written under unconditional surrender agreement in turn US would serve as Japan protector against other nations military aggression. This condition was forced upon Japanese government to be written in Japan constitution and not by the desire from Japan government. Under Pacifist condition, Japan not allow to expand Japan military reach beyond defense Japan from being attack and can't transform Japan military into a expedition force that can wage aggressive war against any nation. Japan completely surrendered Japan military projection and fall under US military umbrella, US obligated to protect Japan against any military attack from any nation not because US obligation is fall under the Mutual Defense Treaty but clearly stated in the Japan Pacifist Constitution.