Another group new to the United States in the antebellum period was the Mexican Americans. Previous to the Texas conflicts and the Me ican War, Me ico was twice as large as it is now. California, Te as, Utah, and many other territories in the West and Southwest of the United States were part of Me ico.

In 1836, however, settlers in Te as from the United States broke their agreement with Me ico to abide by Me ican laws, defeated the Mexican Army, and declared Texas independent. When the United States anne ed Te as in 1845, Me ico and the United States fought a war. The Mexican War ended in 1848, and, under the Treaty of Guadalupe Hidalgo, Me ico had to forfeit its right to parts of California, Nevada, Utah, Arizona, and New Me ico. Shortly after the United States acquire California, gold was discovered in the state.

These vast territories that were now part of the United States contained many former Mexican citizens, who were suddenly Me ican Americans. The transfer of nationhood did not immediately destroy the comple Mex ican society that e isted in those territories. Initially, many Mexicans, especially those from the wealthy and educated upper class, were able to maintain political power. It did not take long, however, for the growing population of settlers from the United States to dominate the area, thus reducing the voice of Mexican Americans in the government. Not until the migration of Mexicans to the United States in the early twentieth century did Me ican Americans regain some of their significance in the former territories of Me ico, in numbers if not in political power.

Another American group new to the West in the antebellum period was the Mormons. In 1830, Joseph Smith founded a religious sect named the Church of Jesus Christ of Latter-Day Saints in Fayette, New York. Smith' s followers were called Mormons after the angel Moroni, who was said to have given Smith the plates, which he published as the Book of Mormon. The Mormons moved west as they faced persecution from Christians and other non-Mormons. This hostility was still present in the western territories, and the Mormons were unsuccessful in their attempts to settle in Ohio, Missouri and Illinois. Smith was killed by a crowd in Illinois in 1844, after which Brigham Young took over leadership. Young led the Mormons to a place of safe haven, and, in 1847, they reached Utah' s Great Salt Lake Valley, which was located in Me ico at the time. There, they founded Salt Lake City, in what would become Utah. Through dedicated hard work, the Mormons were able to convert the seemingly barren land into a prosperous region. The area was organized as the territory of Utah in 1850, with Young as governor. After the Mormons legally abolished the practice of polygamy (a man having more than one wife), the territory was admitted as a state in 1896.

Thus, the western territories of the United States maintained the diversity of many of the eastern states, although the ethnic and religious groups were quite different. Despite official and popular prejudices, many Americans, immigrant and native-born, found new opportunities in the antebellum period. The march of progress continued relentlessly, and though the march of justice and equality was much further behind, it nevertheless did manage to keep moving forward.