The United States bought the Louisiana Purchase from France in 1803.
The agreement transferred a huge territory west of the Mississippi River and east of the Rocky Mountains to the United States. The United States paid $15 million, including the assumption of certain French claims against the United States. The purchase nearly doubled the country’s territorial size.
Thomas Jefferson had initially authorized negotiators James Monroe and Robert Livingston to seek New Orleans and nearby territory. Instead, French foreign minister François Barbé-Marbois offered the entire Louisiana Territory. Napoleon Bonaparte decided to sell partly because France’s plans in North America had been weakened by resistance and disease in Saint-Domingue and by the prospect of renewed war with Britain.
Spain had controlled Louisiana before France regained it in 1800, which causes a frequent mix-up. The treaty was signed on April 30, 1803, announced in the United States on July 4, and ratified by the Senate on October 20. The territory covered about 828,000 square miles, though much of the land was inhabited and governed by Native nations.