Although the Japan Communist Party had been outlawed and forced underground immediately after its foundation in 1922, it continued to gather strength and membership in the volatile social and economic climate of the 1920s Taishō period.
Alarmed by gains that those parties made in the Diet of Japan, the conservative government of Prime Minister Giichi Tanaka, which had retained its majority by only one seat, evoked the provisions of the 1925 Peace Preservation Law and ordered the mass arrest of known communists and socialists and suspected communist and socialist sympathizers.
[1] About 500 of those arrested were eventually prosecuted in a series of open trials held by the Tokyo District Court starting on 15 June 1932, with sentencing on 2 July 1932.
With its connections with the labor movement and other left-wing political parties revealed, the government was able to order the dissolution of the Rōdō Nōmintō (Labor-Farmer Party), the Zen Nihon Musan Seinen Dōmei (All-Japan Proletarian Youth League), and the Nihon Rōdō Kumiai Hyōgikai (Council of Japanese Labor Unions).
Perhaps more importantly, as a consequence of the trials, Prime Minister Tanaka was able to pass legislation to add the provision for the death penalty to the already-draconian Peace Preservation Laws.