The Louisiana Purchase of 1803 was a pivotal agreement in which the United States obtained roughly 827,000 square miles of land from France for around $15 million.

This transaction effectively doubled the nation's size and ensured vital trade routes along the Mississippi River. President Thomas Jefferson aimed to curb French influence in North America. Although there were constitutional worries about the extent of federal authority, the purchase promoted westward expansion and exploration by Lewis and Clark, profoundly influencing the future trajectory of the United States.