Republic of Formosa
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 it being taken over by Japanese troops. The Republic 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 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.
Mexican–American War
Mexico obtained independence from Spain and the Spanish Empire with the Treaty of Córdoba in 1821. It briefly experimented with monarchy, but became a republic in 1824. This government was characterized by instability, leaving it ill-prepared for international conflict when war broke out only two decades later, in 1846. In the decades preceding the war, Native American raids in Mexico's sparsely settled north prompted the Mexican government to sponsor migration from the United States to the Mexican province of Texas to create a buffer. However, the newly named "Texians" revolted against the Mexican government of President/dictator Antonio López de Santa Anna, who had usurped the Mexican Constitution of 1824, in the subsequent 1836 Texas Revolution, creating a republic not recognized by Mexico, which still claimed it as part of its national territory. In 1845, the Texan Republic agreed to an offer of annexation by the U.S. Congress and became the 28th state in the Union on December 29 that year.