The main purpose of U.S. expansion westward in the 19th century was driven by the concept of Manifest Destiny, the belief that Americans were destined to expand across the continent. This expansion aimed to spread democracy and capitalism, as well as to acquire new land for agriculture and settlement. The pursuit of westward expansion led to significant territorial acquisitions, such as the Louisiana Purchase in 1803, the annexation of Texas, and the Oregon Trail migration. However, this expansion came at a considerable cost, including the displacement and violence against Native American populations and the intensification of tensions over slavery, ultimately contributing to the Civil War.