The united small local ruling clans that held military forces on the sea were called kaizoku shu, which were seen in many places in Japan such as in Seto Inland Sea, Kii Peninsular, Ise Bay, and Tokyo Bay.
中世の海辺の小土豪が結合して軍事力をもつようになった海上勢力を海賊衆といい、九州や瀬戸内海、紀伊半島、伊勢湾、東京湾など日本各地で見られた。