The doctrine of Manifest Destiny served to justify the expansion of the United States across North America in the 19th century. It embodied the belief that Americans were divinely ordained to spread democracy and capitalism throughout the continent. Advocates argued that such expansion was both a right and a duty, fostering a sense of national mission. This ideology became the rationale for territorial acquisitions, including the annexation of Texas and the Oregon Trail migration. However, it also contributed to conflicts with Native Americans and tensions over slavery, setting the stage for significant social and political upheaval in the nation.