The United States signed the Louisiana Purchase treaty with France in 1803.
The treaty was signed in Paris on April 30, 1803, by Robert Livingston and James Monroe for the United States and François Barbé-Marbois for France. The agreement transferred a vast territory west of the Mississippi River to the United States for $15 million.
The purchase was shaped by Napoleon Bonaparte’s decision to abandon plans for a French empire in mainland North America. President Thomas Jefferson had initially authorized negotiations focused on New Orleans, whose port was vital to commerce from the interior. The unexpectedly broad French offer led the American negotiators to accept the entire territory.
The land later contributed to all or parts of 15 present-day U.S. states. The treaty was announced publicly on July 4, 1803, and the transfer was formally completed later that year. It is often described as doubling the area of the United States, although its exact size depended on the boundaries used.