Westward expansion in American history exploded for several reasons. First, it came from population pressure and the desire for more land, particularly quality farmland. Expansion was also motivated by religious and civic ideology and conflicting forces over the question of slavery and its continued existence. According to UShistory.org, expansion grew with the discovery of gold in the western territories.
With the Louisiana Purchase and subsequent land acquisitions, U.S. territory grew exponentially in the first half of the 19th century. Populations huddled on the east coast saw grand opportunities to move into more expansive areas where land was cheap and more arable than it was back east, particularly in New England. As noted by UShistory.org, “the desire for land brought aspiring homesteaders to the frontier. When gold was discovered in California in 1848, the number of migrants increased even more.”
Ideology also functioned powerfully. With Manifest Destiny and the Monroe Doctrine, many Americans came to feel entitled to take land in the west, that it somehow fundamentally belonged to them. This sense of destiny was often abetted by a prevailing sense of racial superiority over the peoples who inhabited those territories. Native Americans were considered savages, and economic motives for expansion were thus further justified by the effort of “civilizing” them and converting them to Christianity.
Slavery was yet another factor. By the mid-19th century, debates over slavery in Congress were extremely contentious. Several compromises narrowly avoided conflict, each trying to preserve the tenuous balance between free and slave states. With the western territories, each side saw the opportunity to spread its particular agenda. Nowhere perhaps was the result more devastating than in Kansas, where pro-slavery and anti-slavery settlers clashed in a violent confrontation over the future status of the state. This became known as “Bleeding Kansas,” as stated by the American Anthropological Association.