Japan had a pacifist "constitution" long before 1947, when the current one went into effect. It was issued in the year 604, its author so esteemed, in his own time and since, as to merit the posthumous name Shotoku Taishi (Crown Prince Sage-Virtue). His lifetime (574-622) spanned an early phase of Japan's astonishing leap from prehistory to history, barbarism to civilization, inchoate nature worship to the Buddhism and Confucianism it was just starting to absorb under the generously proffered, gratefully accepted tutelage of its vast and mighty neighbor, civilization itself to dazzled Japanese eyes — China.
Shotoku himself was a great student and sponsor of Chinese learning. Article 1 of his 17-article constitution is Confucian to the core: "Harmony should be valued and quarrels avoided. ... When superiors are in harmony with each other and inferiors are friendly, then affairs are discussed quietly and the right view of matters prevails."
Two decades after Shotoku's death there occurred the famous Taika Reform. Beginning in 645, it transformed Japan — in theory — from a hodgepodge of independent clans into a unified nation, China being the model. "Under the heavens there is no land that is not the emperor's," reads a recurring phrase in contemporary annals. Clan leaders, no longer rulers, became bureaucrats, showered with titles and court ranks but stripped of independent power. From now on what authority they wielded was — again, theoretically — exercised in the Emperor's name, not their own. Article 3 of Shotoku's constitution provides the framework: "Do not fail to obey the commands of your Sovereign. He is like Heaven, which is above the Earth, and the vassal is like the Earth, which bears up Heaven. When Heaven and Earth are properly in place, the four seasons follow their course and all is well in Nature."