The Louisiana Purchase, completed in 1803, significantly expanded the territory of the United States, doubling its size and facilitating westward expansion. Acquired from France for approximately $15 million, the territory included land that would eventually become 15 states, providing vast resources and fertile land. This purchase also strengthened the concept of "Manifest Destiny," the belief that the U.S. was destined to expand across the continent. The acquisition raised questions about slavery in the new territories, contributing to the tensions that eventually led to the Civil War. It was a landmark event that shaped the future of the nation.