Nicholas Kristof wrotee in New York Times (September 10, 2010)
whether or China has a better claim to the Diaoyui Islands. He said as follows:
My feeling is that it's China, although the answer isn't clearcut. Chinese navigational records show the islands as Chinese for many centuries, and a 1783 Japanese map (re: "Sankoku Tsuran Zusetsu" published by prominent military scholar Hayashi Shihei) shows them as Chinese as well. Japan purported to "discover" the islands only in 1884 and annexed them only in 1895 when it also grabbed Taiwan. (You can also make a case that they are terra nullis, belonging to no nation.)
The best approach would be for China and Japan to agree to refer the dispute to the International Court of Justice, but realistically that won't happen. And since some believe that the area is rich with oil and gas reserves, the claims from each side have become more insistent.
As Chinese nationalism grows, as China's navy and ability to project power in the ocean gains, we could see some military jostling over the islands. You read it here first.