Upon his return, he contributed to a divide within the left-wing movement between moderate social democrats and the more radical advocates of direct action, the latter of whom he supported. The growth of the 'direct action' faction led to the banning of the Japan Socialist Party in February 1907, and is arguably the beginning of Japan's modern anarchist movement. He was executed for treason by the Japanese government in the High Treason Incident in 1911, under suspicion of being involved in a bomb plot.