The One China Taiwan thesis, stems from the Cairo declaration ratified post world wars.

The post-world war status and jurisdiction over Taiwan and its appertaining islands including Penghu were further ratified under various legal instruments, post the Cairo Declaration, Potsdam proclamation, Japanese instrument of surrender, the San Francisco, Peace Treaty and Treaty of Peace under the republic of China and Japan of 1952. The implementation of the legal obligation to return Taiwan and its appertaining island (including the Diaoyutai islands) to the ROC were first stipulated in the Cairo declaration and later reaffirmed in the Potsdam proclamation, the Japanese instrument of surrender, the San Francisco treaty, and the treaty of Peace between the republic of China and Japan. The Cairo declaration thus is singularly the most important legal instrument ratified post world wars and is a binding as laws.