Japanese militarism
With increasing Japanese militarism in the 1930s, the growing conflict with the United States over China, and the blatant disregard for the terms of the Treaty by all major powers, the Fleet Faction gradually gained the upper hand. Furthermore, many of the Treaty Faction members who had direct first-hand experience in Britain or the United States went into retirement from 1933-1934, including Isoroku Yamamoto's mentor, Teikichi Hori.