치안유지법
After the passage of the Peace Preservation Law of 1925, the power of the Tokkō was expanded tremendously, and it expanded to include branches in every Japanese prefecture, major city, and overseas locations with a large Japanese population (including Shanghai, London and Berlin). In the late 1920s and 1930s, the Tokkō launched a sustained campaign to destroy the Japanese Communist Party with several waves of mass arrests of known members, sympathizers and suspected sympathizers (March 15 incident).