The Louisiana Purchase, finalized in 1803, dramatically changed the size and scope of the United States by effectively doubling its territory. The U.S. acquired approximately 828,000 square miles of land from France, which included parts of what are now 15 states. This acquisition granted the U.S. control over the vast Mississippi River Valley and opened up opportunities for westward expansion. The Purchase not only enhanced resource availability and agricultural prospects but also raised questions regarding slavery's expansion into new territories, ultimately contributing to the sectional tensions that would lead to the Civil War.