On the first day of 1946, four months after the surrender, the Showa emperor issued a rescript on the construction of a new Japan. Most of it concerns national reconstruction, and it opens by quoting the Charter Oath of 1868. Near the end comes the passage that gave it its popular name: that the ties between the throne and the people do not depend upon mere legends and myths, and are not predicated on the false conception that the emperor is a manifest deity and that the Japanese people are superior to other races and destined to rule the world.
It was issued during the American occupation and its drafting involved occupation officials as well as Japanese ministers, with an English version prepared alongside the Japanese. Two weeks earlier the occupation had issued the directive ending state support, supervision and propagation of Shinto, removing the financial and administrative basis of the shrine system. The rescript and the directive belong together as the dismantling of the pre-war arrangement.
The popular name, ningen sengen, declaration of humanity, is not the document's title and was applied by the press. That matters, because the label states something broader and cleaner than the text, and most people who know of the declaration know the label rather than the words.