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.
Alta California
Mexico gained independence from Spain in 1821 upon conclusion of the decade-long Mexican War of Independence (not acknowledged by Spain until 1836). As the successor state to the Viceroyalty of New Spain, Mexico automatically included the provinces of Alta California and Baja California as territories. Alta California declared allegiance to the new Mexican nation and elected a representative to be sent to Mexico. On November 9, 1822, the first legislature of California was created. With the establishment of a republican government in 1824, Alta California, like many northern territories, was not recognized as one of the constituent States of Mexico because of its small population. The 1824 Constitution of Mexico refers to Alta California as a "territory".