At the end of WW2, Japan stated that they would make war no more. When Japan puts out a decree like that it's not just idle talk. It's a declaration of a change in the way its culture is to be configured.
Yes; an entirely voluntary change of culture and article 9 had nothing to do with that.
It did and was passed in 1947. The US pressured Japan to enact it when they occupied Japan post WW2.
