Many moons ago, the islands at the end of the Southern tip of Japan known as the RyuKyu Kindgom were not part of Japan. In 1609 the Japanese Satsuma clan invaded the islands presumably because they wanted a bit of the lovely emerald water. in 1879 following the Meiji restoration, Japan decided that they wanted to keep the RyuKyu kingdom for their own and from then on it became known as Okinawa prefecture.
At the end of World War II in 1945, Okinawa was under the administration of the United States - I think they wanted some of that emerald water too. During this time, the US established a few military bases which the locals have been complaining about for years. The US eventually responded by saying that they would relocate a particular base but that Japan would have to pay for the expenses - I cant remember the amount but it was enough to buy a small moon.
Okinawa was handed back over to Japan on May 1972.