American drafting of the constitution
The constitution was drafted by a group of young Americans in their 20s and 30s, based on a dozen constitutions around the world, including that of the U.S., within a week in 1946 and implemented in 1947. Despite some dissent from certain Japanese social groups, it has not been revised since then.
Despite the conflicts between the Japanese and American sides--the Japanese wanting to preserve as many pre-war elements, including the pre-war status of the emperor-- the U.S. tried to appeal to the Japanese by choosing Prince Konoe, one senior Japanese statesman friendly to the occupation forces, to be in charge of the constitution preparation (later on Konoe was charged as a Class A war criminal because he was prime minister twice during the war). The initial choice of Konoe was a PR move: to make constitution more receptive in Japan. The very choice of Konoe who was later indicted as war criminal questioned the seriousness of intention on side of Americans.
Despite this initial PR move, the U.S. did not try out a mixed committee made up of both sides. It would be difficult to find common ground: one issue could be the emperor’s divinity; it would also be difficult to find suitable Japanese to do it, as most of the elites were guilty of war. Also sharp differences eixsted between the American and Japanese visions of future Japanese society and politics.