Taiwan was handed back to China at the end of the second world war, but the islands remained under the control of the Americans, who administered them as part of the Okinawa island chain.

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For example, if the Soviet Union had signed a treaty agreeing to sell back to Japan the portion of the Kurile Islands it seized at the end of World War II, that treaty would automatically be binding on Russia and Japan.

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The incident came on the day the Japanese government sets aside for an annual rally demanding the return of territories that Russia took over from Japan at the end of World War II and as Russia was conducting scheduled military exercises around those islands.

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