The Okinawa War of Ten Years (1978)

After World War II, when Okinawa was under control of the United States, the local yakuza prospered. But when Okinawa is returned to Japan, the mainland yakuza tries to take over; the local yakuza tries to compete. Now sides are drawn among the local yakuza guys who used to be best friends since their childhood, and brother fights brother. It results in the biggest yakuza war in Okinawa.