With the end of the Second World War (1939-1945), in 1947 Japan adopted a new Constitution, known as one of the great symbols of the peaceful ideals since its establishment, due to Article 9 – where the country’s military powers are restricted. For this reason, any attempt to revise the Constitution has an impact both domestically, regionally and internationally. However, it is necessary to open the black box to examine whether the Japanese Constitution is indeed guided by pacifism. In the light of the perceptions of the need for a country to respond to the threats of the international system, and questioning niptical pacifism, this article revises the history of the Constitution of Japan and its self-defence forces in order to discuss the behaviour of the archipelago, especially in the 21st century. The hypothesis underlying this article is that, throughout history, the Japanese Government’s interpretations of the Constitution and its defence forces were and are necessary in the face of the transformations of the international system, which boosts the need for document flexibility and the strengthening of the capabilities of its defence forces.