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.
San Luis Obispo, California
When the Mexican War of Independence from Spain broke out in 1810, all California missions had to become virtually self-sufficient, receiving few funds or supplies from Spanish sources. Beginning soon after Mexico won her independence from Spain in 1821, anti-Spanish feelings led to calls for expulsion of the Spanish Franciscans and secularization of the missions. Because the fledgling Mexican government had many more important problems to deal with than far-off California, actual secularization didn't happen until the mid-1830s.