Taiwan  was first populated by Austronesian people and was colonized by the Dutch, who had arrived in 1623. The Kingdom of Tungning, lasting from 1661 to 1683, was the first Han Chinese government to rule Taiwan. From 1683, the Qing Dynasty ruled Taiwan as a prefecture and in 1875 divided the island into two prefectures. In 1885 the island was made into a separate Chinese province to speed up development in this region. In the aftermath of the First Sino-Japanese War, Taiwan and Penghu were ceded by the Qing Dynasty to Japan in 1895. Japanese troops in Taiwan surrendered to the Republic of China at end of World War II, putting Taiwan under a Chinese government again after 50 years of Japanese rule. The ROC would then claim sovereignty on the basis of the Qing dynasty's administration, Cairo Declaration, Potsdam Declaration, and Japanese Instrument of Surrender, but this became contested by pro-independence groups in subsequent years due to different perceptions of the said documents' legality. Upon losing the Chinese civil war in 1949, the ROC government retreated to Taipei, and kept control over a few islands along the coast of mainland China and in the South China Sea. The People's Republic of China  was established in mainland China on 1 October 1949, claiming to be the successor to the ROC. Quemoy, Matsu and Wuchiu on the coast of Fukien, Taiping and Pratas in the South China Sea, are part of the ROC's present territory, but were not ceded to Japan. Some arguments supporting the independence of Taiwan do not apply to these islands.
Answer this question: How many years elapsed between Japan's invasion, and the ROC's defeat in the Chinese civil war?
54