The Japanese invasion of Taiwan, also known as Yiwei War in Chinese, was a conflict between the Empire of Japan and the armed forces of the short-lived Republic of Formosa following the Qing dynasty's cession of Taiwan to Japan in April 1895 at the end of the First Sino-Japanese War. The Japanese sought to take control of their new possession, while the Republican forces fought to resist Japanese occupation. The Japanese landed near Keelung on the northern coast of Taiwan on 29 May 1895, and in a five-month campaign swept southwards to Tainan. Although their advance was slowed by guerrilla activity, the Japanese defeated the Formosan forces whenever they attempted to make a stand. The Japanese victory at Baguashan on 27 August, the largest battle ever fought on Taiwanese soil, doomed the Formosan resistance to an early defeat. The fall of Tainan on 21 October ended organised resistance to Japanese occupation, and inaugurated five decades of Japanese rule in Taiwan.

The Republic of Formosa was a short-lived republic that existed on the island of Taiwan in 1895 between the formal cession of Taiwan by the Qing dynasty of China to the Empire of Japan by the Treaty of Shimonoseki and its being taken over by Japanese troops. The Republic lasted 151 days; it was proclaimed on 23 May 1895 and extinguished on 21 October, when the Republican capital Tainan was taken over by the Japanese. Though sometimes claimed as the first East Asian republic to have been proclaimed, it was predated by the Lanfang Republic in Borneo, established in 1777, as well as by the Republic of Ezo in Japan, established in 1869.