The Chinese had those islands or rather claimed them in the 13th and 14th century. Japan took control of them in the late 1800's and China was in no position to do anything about it. Japan gave it up at the end of ww2 but in China's mind it was not Japans to give up since it was stolen from them. The U.S.A. gave control back in the seventies to Japan. China has historic claim and its none of the Wests business.