Mesoamerican chronology
Mexico became independent from Spain in 1821, with some participation of indigenous in decade-long political struggles, but for their own motivations. With the fall of colonial government, the Mexican state abolished distinctions between ethnic groups, that is the separate governance for indigenous populations in the "República de Indios". The new sovereign country made, in theory at least, all Mexicans citizens of the independent nation-state rather than vassals of the Spanish crown, with different legal standing. A long period of political chaos in the post-independence period among white elites largely did not affect indigenous peoples and their communities. Mexican conservatives were largely in charge of the national government and kept in place practices from the old colonial order. However, in the 1850s, Mexican liberals gained power and attempted to formulate and implement reforms that did affect indigenous communities, as well as the Catholic Church. The Mexican Constitution of 1857 abolished the ability of corporations to hold land, which aimed at taking assets out of the hands of the Catholic Church in Mexico and forcing indigenous communities to divide their community-held lands. Liberals' aimed at turning indigenous community members pursuing subsistence farming into yeoman farmers holding their own land. Mexican conservatives repudiated the liberal reform laws since they attacked the Catholic Church, but indigenous communities also participated in a three-year civil war. In the late nineteenth century, liberal army general Porfirio Díaz, a Mestizo did much for modernizing Mexico and integrating it into the world economy, but there were renewed pressures on indigenous communities and their lands. These exploded in certain areas of Mexico during the ten-year long civil war, the Mexican Revolution (1910-1920). In the aftermath of the Revolution, the Mexican government attempted simultaneously shore up indigenous culture, while at the same time also attempting to integrate the indigenous as citizens of the nation, turning indigenous into peasants ("campesinos"). This has proved more difficult than policy planners imagined, with resilient indigenous communities continuing to struggle for rights within the nation.
Presidency of James K. Polk
The United States had been the first country to recognize Mexico's independence following the Mexican War of Independence, but relations between the two countries began to sour in the 1830s. In the 1830s and 1840s, the United States, like France and Britain, sought a reparations treaty with Mexico for various acts committed by Mexican citizens and authorities, including the seizure of American ships. Though the United States and Mexico had agreed to a joint board to settle the various claims prior to Polk's presidency, many Americans accused the Mexican government of acting in bad faith in settling the claims. For its part, Mexico believed that the United States sought to acquire Mexican territory, and believed that many Americans filed specious or exaggerated claims. The already-troubled Mexico–United States relations were further inflamed by the possibility of the annexation of Texas, as Mexico still viewed Texas as an integral part of their republic. Additionally, Texas laid claim to all land north of the Rio Grande River, while Mexico argued that the more northern Nueces River was the proper Texan border. Though the United States had a population more than twice as numerous and an economy thirteen times greater than that of Mexico, Mexico was not prepared to give up its claim to Texas, even if it meant war.