The significance of the Louisiana Purchase in 1803 lies in its dramatic expansion of U.S. territory, effectively doubling the nation's size. Acquired from France for $15 million, it provided access to vast lands rich in natural resources and enhanced westward expansion opportunities. This transaction not only secured crucial territory for agriculture and settlements but also facilitated the idea of Manifest Destiny—the belief that Americans were destined to expand across the continent. The Purchase played a pivotal role in shaping the future of the United States and its growth as a nation.