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沖縄県 (okinawa-ken), which is "Okinawa Prefecture", omitting the last Kanji 県 (ken) makes it 沖縄 (okinawa).
Okinawa is an island
Okinawa is a part of Japan so yes, Okinawa was in WWI.
Okinawa is in the northern hemisphere.
Okinawa is in Japan not China.