The significance of the Louisiana Purchase in the context of U.S. expansion lies in its vast territorial gains and implications for the future of the nation. In 1803, the U.S. acquired approximately 828,000 square miles of territory from France, effectively doubling the size of the country. This acquisition not only improved land access for settlers but also set the stage for westward expansion, fueled the concept of Manifest Destiny, and influenced economic growth. Additionally, it spurred explorations, such as those led by Lewis and Clark, helping to map the new territory, establish American claims in the Pacific Northwest, and cultivate American identity in the burgeoning frontier.