Ultimately, American westward expansion was driven by the belief that the land west of the Mississippi River held better opportunities.
By the 1830s, the East Coast was beginning to feel overcrowded and the soil overworked. Farmers dreamed of huge, relative untouched, fertile pieces of land to work west of the Mississippi. Additionally, eastern states had well-established political machines in place, and citizens wanted to forge new states where they would have a hand in building the eventual political representation.
By the 1840s, the Oregon Trail began, which formed a viable path to the Oregon Territory and the Pacific Ocean for families to travel by covered wagon. Many made it all the way, but a significant population stopped short and settled the land in the Midwest and Rocky Mountain regions. A motivating driver by this point was the idea of Manifest Destiny, which was the idea that American culture and politics were sacred and morally correct, and Americans had the duty, handed down by a higher power, to spread American way of life from the Atlantic Ocean to the Pacific Ocean.
In the late 1840s, a massive gold rush to California convinced people to go west, driven by dreams of financial prosperity.
Aside from covered wagons, travelers also relied on the steamboat to travel rivers. Others traveled west to practice their religion. The best example of this is the Mormons settling in Utah.
This westward expansion was supported through the American government’s ability to secure new territories through both war and diplomacy.
By the 1830s, the United States government was pushing a program of Westward expansion and encouraging white settlers to move west of the Mississippi River. By 1824, 30% of the population of the United States lived in the region between the Appalachian Mountains and the Mississippi River. A slow move west had already been occurring, and by the 1830s, families cited overcrowding, depleted soil, urbanization, lack of economic opportunities, and undesirable politics as reasons to move West, away from the dense and saturated East coast. This move directly coincided with further genocide and displacement of indigenous peoples as white setters colonized land and brought the force of the United States's militias westward.
By the 1830s, westward-bound settlers traveled by river via steamboat and canalboat and over land on trails via horse/oxen-drawn wagons and on foot. Many of these settlers moved to Ohio, Indiana, Illinois, and Oklahoma. By the 1840s, as white settlers moved West, the United States began to secure more territory through its war with Mexico. In 1841, the Oregon Trail opened and over the next 20 years, over 300,000 people traversed the trail by wagon. Many of these travelers settled in Oregon Country. Many others settled in Colorado, Nevada, Wyoming, California, and Texas.
By 1845, the idea of Manifest Destiny, in which white settlers believed they had a divine right, given by their christian god, to expand westward (killing and displacing thousands of indigenous people as they went) became an accepted term and racist perspective.
Americans moved west of the Mississippi River in the 1830s-40s for many reasons. One reason was the American people believed the Americans should control the land from the Atlantic Ocean to the Pacific Ocean. This belief, called Manifest Destiny, encouraged the United States to acquire land and to have American people move to these lands. There was a belief that the American way of life was the best way of life, and therefore, the Americans should control this land.
There were other reasons for the westward movement. Some people moved westward because they saw a great deal of economic opportunity. These people wanted to farm their own land or to start their own businesses. They believed the western lands were a golden area filled with many new economic opportunities. Some people were also looking for a sense of adventure. Moving westward fulfilled this desire for adventure. The Mormons moved to Utah in the hope that they could practice their religion without harassment.
Westward movement was accomplished in several ways. Texas was added to the United States in 1845. The United States fought Mexico in the Mexican-American War and gained a great deal of land from Mexico in 1848. The United States also divided the Oregon Territory with Great Britain. As more people moved to these western lands, railroads and roads were built to facilitate the westward movement. People moved to the Great Plains and also to the areas near the Pacific Ocean, such as Oregon and California. People also moved to areas where minerals were found. For example, California’s population grew dramatically when gold was discovered there.
https://www.historynet.com/westward-expansion
Americans moved west of the Mississippi River for the same reason they always did—greater opportunity. Mexico initially welcomed Americans in Texas until they realized that the new immigrants would not give up their Protestant faith or their slaves. Texans finally declared their independence from Mexico and created the Republic of Texas, which would be annexed into the United States in 1845. Settlers moved into the Willamette Valley in Oregon following the Oregon Trail via wagon train from 1840 to 1860. They moved here looking for cheap, fertile land. The emigrant flow only increased once the United States gained clear title to the territory in 1846. The Mormons of Nauvoo, Illinois moved to Salt Lake starting in the 1840s in order to find a place to practice their faith without persecution. This group of emigrants were famous for taking large handcarts with them to move their supplies. Finally, the California Trail began in 1849 after John Sutter found gold in the territory. After the discovery, thousands came from all over the world—some came via the overland route which was also part of the Oregon Trail, while others took a sea and land route with a portage through Panama. They had to take a land route through Panama as there was no canal there back then. Others took clipper ships around the tip of South America to reach California. Once there, only a minority struck it rich, though many realized that the region could grow crops nearly year-round and there was a good market in selling miners supplies and food.