The 1803 Louisiana Purchase added territory to the United States for $15 million.
The agreement transferred approximately 828,000 square miles of territory from France to the United States. The land stretched from the Mississippi River to the Rocky Mountains and from the Gulf of Mexico toward the Canadian border, though its boundaries were not perfectly defined at first.
President Thomas Jefferson authorized the negotiations, and Robert Livingston and James Monroe concluded the deal with France. Napoleon Bonaparte's government agreed to sell after France's plans in North America weakened, especially following the loss of Saint-Domingue and the renewed war with Britain.
The purchase more than doubled the area of the United States, but it also raised constitutional and political questions. Jefferson favored a strict interpretation of federal powers, yet he supported the purchase because of its strategic and economic importance. The deal is often confused with the later Alaska Purchase, which cost $7.2 million.