As late as 1840, when Americans talked about the West, they referred to the area between the Appalachian Mountains and the Mississippi River, and perhaps a slight bit beyond. The areas of Texas, New Mexico, California, and Oregon were regarded as a vast, unknown, and shadowy region, even by the nations with claims there. Spain, and after 1821, Mexico, claimed Texas, New Mexico, and California, and Oregon was jointly occupied by the United States and Great Britain. These areas had, for the most part, remained devoid of settlers throughout the expansion boom of the 1820s and 1830s.

Trappers and traders made the first forays into the Far West during the 1820s. Fur trappers in California and Oregon traded cattle hides with eastern merchants for manufactured goods. The Rocky Mountains of Colorado and Utah saw the rise of the beaver trapping industry. The British Hudson's Bay Company established a similar pattern of trade. Farther South, the Santa Fe Trail linked St. Louis and Santa Fe, establishing strong economic connections between the regions surrounding the endpoints of the trail. After the Panic of 1819, merchants saddled with unsold goods loaded up wagons and traveled to Santa Fe where they traded for mules and New Mexican silver. Mexico benefited from this trade, as many goods made their way to the Mexican interior, and encouraged interaction with American traders. As a result, the Mexican silver peso soon became the standard medium of exchange in Missouri.

During the 1820s and beyond, glowing reports of the Southwest led to a large influx of American settlers, especially into Eastern Texas. Meanwhile, the Spanish, and later Mexican, government attempted to promote the settlement of California and New Mexico by Hispanic people, largely through the use of the mission. Missions were established all along the California coast and into the interior of Texas and New Mexico. The missionaries tried to convert the region's Indians, and built towns around their missions. By 1823, over 20,000 Indians had converted and were living in the missions of California.

Due to Mexico's expenditure of time, energy, and funding on its successful fight for Independence in 1821, the mission system installed by the Spanish declined during the late 1820s and 1830s. The Mexican government "secularized" the missions during the late 1820s and 1830s by giving their lands to government officials and ranchers. Many Indians left the missions and returned to their tribes. During the 20s and 30s, these tribes, in opposition to Mexican efforts at settlement, terrorized the Mexican frontier, stealing cattle and carrying off women and children. Apache and Comanche Indians attacked New Mexico and Texas, sweeping southward into Mexico. They advanced within 150 miles of Mexico City before being turned back. This turmoil in the Southwest made the settlers and Mexican government helpless to stop the advances of American settlers.

Traders posed little threat to the Mexican provinces of the Southwest. The Mexican people of California and New Mexico depended heavily on American trade for manufactured goods, and the governments of both territories relied on customs duties generated by the trade. Although relations were for the most part mutually beneficial, there was always potential for conflict between American and Mexican settlers. Spanish speaking, Roman Catholic, and accustomed to a hierarchical society, the Mexicans presented a sharp contrast to the Protestant, individualistic American settlers. At first, American traders and lone settlers conformed to the life of the Hispanic settlers. However, as more and more Americans moved west, and separated communities began to spring up, the potential for conflict grew. Still, the economic ties between the two groups kept them on mostly amiable terms, and the influx of American trade, capital, and know-how into the Far West led to the beginnings of modernization.

No one factor led to the early settlement and organization of the Far West more than the establishment of Spanish missions early in the nineteenth century. The Spanish mission was a tool for advancing political, economic, and religious goals. The missions were staffed by Franciscan priests who were paid by the government to convert Native Americans and settle them on mission lands. The mission at once became a center for trade from the East, oversaw the development of local government, and encouraged settlement of the Indians on mission lands in order to create a thriving class of workers able to aid in the development of the untamed West. Even as their direct impact waned due to "secularization" and the enmity of the Indians, their influence over the permanent settlement of the West remains clear even today in the names of towns and cities such as San Francisco and San Diego, scattered throughout the American West.

Mexican policy was partially responsible for the rise of conflict between the Indians and Hispanic settlers. The secularization of the missions had resulted in some ranchers turning Indians into slave laborers. Many Indian villages in California and New Mexico were the targets of frequent raids by settlers seeking domestic servants. Hispanic settlers gave little thought to riding into an Indian village and absconding with Indian women and children. Relations between the two groups grew progressively worse as time went by, and soon the Indians saw the Mexican government as the bastion of evil.

Since the Mexican army refused to aid settlers on the frontier, the territory was under populated. In 1836, New Mexico had 30,000 Hispanic settlers, but California had only 3,200, and Texas, only 4,000. These sparse, unsupported settlements soon were overwhelmed by the arrival of American settlers. To the Americans watching the development of what is now the Midwest, the Far West seemed the next wild frontier. Following stories of adventure and bountiful resources, Americans began to flow into the Southwest.