The historical importance of the Louisiana Purchase, completed in 1803, lies in its significant expansion of U.S. territory. The United States acquired approximately 827,000 square miles of land from France for $15 million, effectively doubling the size of the nation. This acquisition not only opened vast tracts of land for settlement and agriculture but also secured critical access to the Mississippi River and New Orleans, vital for trade. The purchase set a precedent for westward expansion and Manifest Destiny, shaping the nation's future and its geopolitical landscape. It also raised questions about the extension of slavery into new territories.