Manifest Destiny was a 19th-century belief that the expansion of the United States across the American continent was both justified and inevitable. This idea suggested that Americans were destined by God to spread democracy and capitalism throughout the continent, which many viewed as a moral obligation. The concept played a significant role in the westward expansion of the United States, influencing events such as the Louisiana Purchase, the Oregon Trail, and the Mexican-American War. It contributed to the displacement of Native American tribes and raised questions about the extension of slavery into new territories.