The American Revolution (1765-83), French Revolution (1789-99) and Napoleonic Wars (1803-1815) shook up the old Monarchy based order, ushering in an age of Nationalism and 'Independence'. To be independent, you have to be able to define where you end and where something else begins. The elites of the old world wanted to rule everybody. If the body are ruling, that needs a separation from the every.
As Spain's global power fell, Mexico declared independence in 1810. As with most places, independence led to years of internal conflict as sub-identities asserted themselves. Unable to convince many Tejano to move to Texas, soon they were outnumbered by immigrating Anglos. In 1836, the Republic of Texas declared independence. The government has actively encouraged the Mexican identity (a synthesis of European and Indigenous) over racial or ethnic groups not asking for information from 1921-2010. 22% of the population self-identifies as indigenous based on speaking one of 62 indigenous languages. 83% of the population give Roman Catholicism as their religion and 99% speak Spanish.
Evolution of Territorial Independence