Okinawa was a US colony from the end of WW II until 1973. Per Wikipedia, "As of 2014 the US still maintains Air Force, Marine, Navy, and Army military installations on the islands. These bases include Kadena Air Base, Camp Foster, Marine Corps Air Station Futenma, Camp Hansen, Camp Schwab, Torii Station, Camp Kinser, and Camp Gonsalves. The area of 14 U.S. bases are 233 square kilometres (90 sq mi), occupying 18% of the main island. Okinawa hosts about two-thirds of the 50,000 American forces in Japan although the islands account for less than one percent of total lands in Japan."

Although Okinawa is prefecture of Japan, the Okinawans are ethnically distinct from other Japanese and already feel underrepresented in the national interest. Mainland Japanese opposed introduction of US nuclear weapons to their part of the nation, but allowed them on Okinawa from 1954 to 1972.

So they've got something to complain about, in addition to the bad behavior of some GIs and contractors.