In terms of international law, Taiwan has not been a part of China since 1895. Taiwan has become a country through a continuous process of evolution. In the process of democratization and Taiwanization -- and thanks to the effective self-determination of its people -- Taiwan has evolved from a territory under military occupation following World War II to a country with the sovereignty and independence of a nation-state. This theory of Taiwan's evolution into a state conforms to historical developments, changing political conditions and the dynamic character and principles of international law. I support this theory of evolved nationhood, which I described previously on this page ("The evolution of Taiwan's statehood," Aug. 9, page 8).
There are other theories regarding Taiwan's international legal status in addition to the evolutionary theory of statehood.
One theory is that Taiwan is part of China. This is what the People's Republic of China (PRC) argues, citing history, the Cairo Declaration, the Potsdam Declaration, succession to the Republic of China (ROC), UN General Assembly Resolution 2758, and that "Taiwan is an internal affair of China," to support its position.
Yet Beijing's argument fails the tests of both reality and international law, for the following reasons.
One, Taiwan has been fought over by foreigners for hundreds of years, while the Taiwanese have battled for their existence and self-governance. There have been the indigenous peoples and the Han Chinese, the Dutch and Spanish colonial empires competing over Taiwan, Cheng Cheng-kung's (鄭成功) family dynasty, the nominal rule of the Qing dynasty (which ceded Taiwan to Japan shortly after making it a province), the brief establishment of the Republic of Formosa, 50 years of Japanese colonial rule and the military occupation following World War II.
Taiwan has evolved into a sovereign and independent nation. Clearly, Taiwan has not been "an inseparable part of China since ancient times."
Two, as for ownership of Taiwan's territory, the Cairo and Potsdam declarations were overridden by the 1951 Treaty of San Francisco with Japan. The Taiwan that Japan gave up in the treaty, including the Penghu Islands, belonged to neither the PRC nor the ROC. No wonder Beijing has avoided bringing up the treaty, which carries the most weight in international law.
Three, when the PRC was established on Oct. 1, 1949, the ROC had "militarily occupied" Taiwan on behalf of the Allied forces but not acquired sovereignty over or ownership of Taiwan. It is impossible for the PRC -- nor does it have the right -- to inherit powers that the ROC never had.
Four, UN Resolution 2758 does not accede that Taiwan is a part of the PRC.
Five, since its founding the PRC has never effectively controlled, ruled or exercised jurisdiction over Taiwan. By international law, Taiwan is not an "internal affair of China" but a question of international concern.
Taiwan and the PRC are two different countries, therefore the dispute over Taiwan's legal status involves interpretations of international agreements and international law; the PRC's threats toward Taiwan jeopardize peace in the Asia-Pacific region and the world; China's "Anti-Secession" Law violates international law; and Taiwan's future involves the effective implementation of the principles of self-determination enshrined in international law, and will affect the fundamental human rights and wellbeing of 23 million Taiwanese.