The significance of the Louisiana Purchase, completed in 1803, lay in its vast territorial expansion of the United States and the implications for westward expansion. The U.S. acquired approximately 828,000 square miles of land from France for $15 million, doubling the size of the nation at the time. This purchase facilitated settlement of the western frontier and the idea of Manifest Destiny, which held that Americans were destined to expand across the continent. It also provided important resources and facilitated economic growth. Additionally, the Louisiana Purchase stirred debates over slavery's expansion into new territories, shaping the political landscape leading up to the Civil War.