The concept of "Manifest Destiny" was based on the belief that Americans were destined to expand across the North American continent. This idea was rooted in the notion that such expansion was not only a right but also a divine obligation, as it was believed to promote democracy and civilization. It influenced American policies in the 19th century, justifying the westward expansion and the acquisition of territories through tactics such as negotiation, war, and annexation, including the annexation of Texas and the Oregon Trail migration. Ultimately, it played a critical role in shaping U.S. history and territorial boundaries.