The United States acquired the Louisiana Territory from France in 1803 through the Louisiana Purchase.
President Thomas Jefferson’s administration negotiated the agreement with France, represented by Napoleon Bonaparte’s government. The United States paid 60 million francs and assumed claims by American citizens against France, for a total value commonly described as about $15 million.
The purchase transferred approximately 828,000 square miles of territory west of the Mississippi River and greatly expanded the young republic. It included land that later became all or parts of 15 U.S. states and two federal territories.
The agreement created constitutional questions for Jefferson because the Constitution did not explicitly describe a power to acquire foreign territory. Congress approved the treaty, and the transfer was completed in December 1803.