Kokuryu-kai (Amur River Society), also know as the Black Dragon Society, was a prominent underground ultra-nationalist group in Japan. It was founded in 1901, and was descended from the Dark Ocean Society. The Black Dragons were infamous for their espionage and sabotage, particularly in China and the United States in World War II. An evolution of the Genyosha group, it helped set the stage for future yakuza practices.