Grande as its southern boundary, while Mexico insisted that the Nueces River was the boundary. In practice, much of the disputed territory was occupied by the Comanche and outside the control of either state, but Texian claims included the eastern portions of New Mexico, which was administered by Mexico throughout this period. Texas was annexed by the United States on December 29, 1845, and was admitted to the Union as the 28th state on that day, with the transfer of power from the Republic to the new state of Texas formally taking place on February 19, 1846. However, the United States inherited the southern and western border-disputes with Mexico, which had refused to recognize Texas's independence or to accept U.S. offers to purchase the territory. Consequently, the annexation led to the Mexican–American War (1846–1848). History Spanish Texas During the late Spanish colonial era, Texas had been one of the Provincias Internas, and the region is known in the historiography as Spanish Texas. Though claimed by Spain, it was not formally colonized by the empire until competing French interests at Fort St. Louis encouraged Spain to establish permanent settlements in the area. The region was occupied and claimed by the existing indigenous groups. Sporadic missionary incursions occurred into the area during the period from the 1690s–1710s, before the establishment of San Antonio as a permanent civilian settlement. Owing to the area's relatively dense Native American populations, its remoteness from the population centers of New Spain, and the lack of any obvious valuable resources such as silver, Texas had only a small European population, although Spain maintained a small military presence to protect Catholic missionaries working among Native American tribes, and to act as a buffer against the French in Louisiana and British North America. In 1762, Bourbon France ceded to Bourbon Spain most of its claims to the interior of North America, including its claim to Texas, as well as the vast interior that became Spanish Louisiana. During the years 1799 to 1803, the height of the Napoleonic Empire in France, Spain returned Louisiana to France, which then promptly sold the territory to the United States. The status of Texas during these transfers was unclear and was not resolved until 1819, when the Adams–Onís Treaty between Spain and the United States ceded Spanish Florida to the United States, and established a clear boundary between Texas and Louisiana. Starting in 1810 with