Article 9 of the Japanese Constitution (日本国憲法第9条 Nihonkokukenpō dai kyū-jō?) is a clause in the national Constitution of Japan outlawing war as a means to settle international disputes involving the state. The Constitution came into effect on May 3, 1947, following World War II. In its text, the state formally renounces the sovereign right of belligerency and aims at an international peace based on justice and order. The article also states that, to accomplish these aims, armed forces with war potential will not be maintained.
However, Japan maintains de facto armed forces, referred to as the Japan Self-Defense Forces, which may have originally been thought of as something akin to what Mahatma Gandhi called the Shanti Sena (soldiers of peace) or a collective security police (peacekeeping) force operating under the United Nations. Source: Wikipedia
Japan adopted pacifist doctrine after it tasted the nuclear weapons. However it’s changing its policy under the stewardship of Mr. Abe. Situation demands different action. Threats from assertive China and unbridled North Korea making things worse for Japan.