【正确答案】Diaoyu Island belongs to China. It is by no means "terra nullius". China is the indisputable owner of Diaoyu Island as it had exercised valid jurisdiction over the island for several hundred years long before the Japanese people "discovered" it. As stated above, voluminous Japanese official documents prove that Japan was fully aware that according to international law, Diaoyu Island has long been part of China and was not "terra nullius". Japan's act to include Diaoyu Island as "terra nullius" into its territory based on the "occupation" principle is in fact an illegal act of occupying Chinese territory and has no legal effect according to international law.
Diaoyu Island has always been affiliated to China's Taiwan Island both in geographical terms and in accordance with China's historical jurisdiction practice. Through the unequal Treaty of Shimonoseki, Japan forced the Qing Government to cede to it " the island of Taiwan, together with all islands appertaining or belonging to it" , including Diaoyu Island. International legal documents such as the Cairo Declaration and the Potsdam Proclamation provide that Japan must unconditionally return the territories it has stolen from China. These documents also clearly define Japan's territory, which by no means includes Diaoyu Island. Japan's attempted occupation of Diaoyu Island, in essence, constitutes a challenge to the post-war international order established by such legal documents as the Cairo Declaration and the Potsdam Proclamation and seriously violates the obligations Japan should undertake according to international law.