Texas includes, more or less, OTL Texas and eastern New Mexico.
Originally settled by Spaniards, after the independence of Mexico, the Mexican government promoted some settlements by Anglos (US naturals).
In 1836, an insurrection by both Anglos (usually known as Texians) and Hispanics against the central government in Mexico, was crushed after a difficult march over the desert by the Mexican Army. Given the hiden support the US government gave the insurrection, a series of incidents almost prompted a war between Mexico and the USA.
In 1838, a binational commition was called to solve the limit conflicts between Mexico and the USA, under the assumption that Texas was not part of the Louisiana Purchase. The result of the commission was accepted by both governments as the definitive limits, a situation that is preserved today as the limits between the USA and the republics of Texas, and Deseret.
During the Great War of 1862, and given the situation in Mexico, a second independence movement took place, and the Republic of Texas was proclaimed in 1864. Mexico recognized the independence of Texas in 1875.
In 1889, Texas was involved in a civil war between the two main parties: the Liberal Party and the Texian Unionist Party. The triumph of the Liberals promoted a greater deal of bilinguism, and the consolidation of Texas as an independent entity.
In 1902, there was a war against Deseret for some border disputes. This war was basically a shooting war and was soon settled by the mediation of the USA and Sonora and Arizona.
Texas fought the Great War of 1935, as an ally of the United States of America.
Political divisions of the nation