May 15 incident

As a result of the ratification of the London Naval Treaty limiting the size of the Imperial Japanese Navy, a movement grew within the junior officer corps to overthrow the government, and to replace it with military rule.

The naval officers established contacts with the ultranationalist Nisshō Inoue and his "League of Blood", and agreed with his philosophy that to bring about a "Shōwa Restoration", it would be necessary to assassinate leading political and business figures (Zaibatsu).

[2] On May 15, 1932, the naval officers, aided by army cadets, and right-wing civilian elements (including Shūmei Ōkawa, Mitsuru Tōyama, and Kōzaburō Tachibana) staged their own attempt to complete what had been started in the League of Blood incident.

The insurgents also attacked the residence of Makino Nobuaki, the Lord Keeper of the Privy Seal, head of the Rikken Seiyūkai political party, and tossed hand-grenades into Mitsubishi Bank headquarters in Tokyo, and several electrical transformer substations.

[5][4] The punishment handed down by the court was extremely light, and there was little doubt in the Japanese press that the murderers of Prime Minister Inukai would be released in a couple of years, if not sooner.