In the Yalta system (including Cairo Declaration and Postan Proclamation), Ryukyu Islands, Taiwan Province Province, four northern islands, Diaoyu Island and Dokdo do not belong to Japan. In the San Francisco Declaration of 195 1, the United States returned the sovereignty of Ryukyu Islands and Diaoyu Islands to Japan, excluding Taiwan Province Province of China. Due to the efforts of fishermen at that time, the sovereignty of Diaoyu Island was not handed over to Japan. The loss of the United States is that it is no longer clear about the ownership of sovereignty and deliberately vague.