History of Hispanic and Latino Americans in the United States
In 1821, Mexico gained independence from Spain, annexing the southwest of the present United States, including Arizona. As missions began to wither, Mexico began auctioning off more land, causing the Pimería Alta and the Apachería to shrink as territory expanded. In the meantime, American mountain men began to enter the region, looking to trap beavers for their pelts. In 1836, Texas declared independence from Mexico and claimed much of the territory in the northern lands of Mexico. When the United States annexed Texas in 1846 over the strong objections of the Mexican government, U.S. troops moved into disputed territory. The hostilities erupted in the Mexican–American War (1846–1848). The U.S. occupied Mexico City and forced the newly founded Mexican Republic to give up its northern half, including the later Arizona.
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.