Japan has had pro-romanization societies since the 1920's, and even during the last attempt at large-scale script reform after the war, it wasn't just the Americans pushing it: Many Japanese were enthusiastic about moving to a phonetic script because they perceived it as more efficient and modern. Likewise, not every American administrator was in favour of reforming away the kanji, far from it.

J. Marshall Unger's Literacy and Script Reform in Occupation Japan is a good treatise on the subject.

EDIT: Also, this was published in 1877 if I did my date conversions right: https://archive.wul.waseda.ac.jp/kosho/bunko17/bunko17_d0035...