Mexico faced serious problems after it became independent from Spain in 1821. After a brief flirtation with monarchy, it became a republic, and a succession of presidents wrangled over whether the new nation should be centralist, with a strong government in Mexico City, or federalist, with considerable autonomy given to the provinces. Mexico's northern provinces, from Texas to California, were underpopulated and difficult to defend, so Mexico initially encouraged American settlement and trade. Americans were also attracted to potentially rich farmland in the Oregon Country in the early 1840s. While settlers moved into the Republic of Texas, the opening of the Oregon Trail marked the beginning of significant migration to the Pacific Northwest as well.
The settlement of Texas. In the last days of colonial rule in Mexico, Spain had accepted a proposal from several American entrepreneurs to bring American settlers into Texas; Mexico renewed the agreement in 1825 with the provisions that all newcomers become Mexican citizens and accept Catholicism. Promoters of American settlement (known as empresarios by the Mexicans), such as Stephen F. Austin, did their jobs well. As many as twenty thousand Americans, along with a thousand slaves, were living in Texas by 1830, mostly southern fanners who found the land cheap and ideal for growing cotton. The growth of the American population, which quickly overwhelmed the group of roughly five thousand Spanish‐speaking Mexicans in Texas ( Tejanos), led Mexico to reverse its “open‐door” policy. The Mexican Congress banned slavery in Texas and prohibited further immigration by American citizens, but settlers, both white and slave, continued to cross the border from the United States. Tensions rose as Americans demanded a greater say in their own affairs.
Texas's independence. In 1834, General Antonio Lopez de Santa Anna seized power in Mexico, determined to exercise greater control over Texas. His attempts to enforce his centralist policies there failed, and in 1835, he led his troops north. The American Texans and Tejanos responded with a declaration of independence (March 2, 1836), but the first confrontation of the Texas Revolution was a disaster for them. Santa Anna's forces completely wiped out the defenders of the Alamo, a mission on the outskirts of San Antonio. Famed frontiersmen Davy Crockett and Jim Bowie died in the fighting. A few weeks later, Santa Anna ordered the execution of all Texas prisoners captured in the Battle of Goliad. The tide decisively turned when Sam Houston, a former governor of Tennessee who had fought with Andrew Jackson, took command of the Texas army. At the Battle of San Jacinto (April 21, 1836), he surprised the Mexican troops, captured Santa Anna, and forced the general to sign a treaty that recognized Texas's independence in return for his freedom. Although Santa Anna repudiated the treaty after he was released, as did the Mexican government, Texas had become a sovereign nation.
While refusing to acknowledge Texas's independence, Mexico still simmered over the location of the border. The Mexican government had long maintained that Texas was part of the province of Coahuila, whose northern boundary was the Nueces River. Independent Texans, on the other hand, claimed the two‐thousand‐mile‐long Rio Grande as their southern and western border. The enormous territory north and east of the Rio Grande remained in dispute until 1846.
The Republic of Texas chose Sam Houston as its first president, created a legislature and court system, and received diplomatic recognition from the United States, Great Britain, and France. Most Texans, however, expected and wanted their independence to be short‐lived. But the Republic's petition for annexation to the United States was refused in 1837, and Texas did not become a state until 1845.
New Mexico and California. In 1821, Mexico opened Santa Fe, one of the oldest European settlements in North America, to U.S. trade. In just a short time, wagon trains carrying American goods were making the long trek from Independence, Missouri, to Santa Fe, along what became known as the Santa Fe Trail. While fewer settlers went to New Mexico than to Texas, the commercial ties were profitable, and more important, the establishment of the trail demonstrated that the Great Plains was not a barrier to westward expansion.
Mexico also began to encourage U.S. trade with California, whose ports had been effectively off limits to foreign shipping during the period of Spanish rule (1769–1821). Agents of New England merchants established offices for the purpose of exchanging a wide variety of American‐made products for California cattle hides and tallow. Many of the agents married Spanish‐speaking Californians, or Californios , and converted to Catholicism. The first Americans to reach California overland were fur trappers and traders, such as Jedediah Smith (1826) and James Pattie (1828), who reached the Mexican province by way of Santa Fe. By the 1840s, two main routes were open to settlers—the Old Spanish Trail from Santa Fe into southern California and the California Trail, an Oregon Trail offshoot that crossed the Sierra Nevada and descended into the Sacramento River Valley. Wealthy Californios and a small number of early American settlers acquired vast estates known as ranchos after Mexico secularized the lands of the Catholic missions in 1834.
Dissatisfaction with the remote Mexican government grew in California throughout the 1830s. A rapid turnover of provincial governors, most of whom knew little about California, exacerbated the negative feelings. By 1845, a native governor, Pio Pico, who was based in Los Angeles, and the Mexican military commandant in Monterey were battling over power. Under these frustrating conditions, many people in California, including the seven hundred or so Americans there, concluded that it was time for a complete break with Mexico, either through independence or by annexation to the United States.
The Oregon Country. American claims to the Oregon Country dated back to Captain Robert Gray's discovery of the Columbia River in 1792 and were reinforced by the expedition of Lewis and Clark to the Pacific (1804–06). The official joint occupation of the territory by the United States and Great Britain worked well until the 1840s, when “Oregon fever” gripped many Americans. Wagon trains, organized in the spring in Independence or St. Joseph, Missouri, transported chiefly young families from the Midwest, who traveled northwest for six months over the Oregon Trail, parts of which had long been in use by trappers and early explorers. These pioneer families traveled along the Platte River, crossed through the South Pass of the Rocky Mountains, and then turned north to follow the Snake and Columbia Rivers to the Willamette Valley. Between 1841 and 1845, an estimated five thousand Americans settled in the Oregon Country, by far the largest number of people to have traveled to the Far West.