The 1803 Louisiana Purchase acquired the territory from France.
The United States negotiated with the French First Republic during the administration of President Thomas Jefferson. Robert Livingston and James Monroe represented the United States, while François Barbé-Marbois negotiated for France. The treaty was signed in Paris on April 30, 1803.
The purchase covered a vast area west of the Mississippi River, including the important port of New Orleans. The United States paid $15 million, and the acquisition nearly doubled the country’s size. It later contributed to the creation of numerous states and territories.
A common mix-up is Spain’s role. Spain had controlled Louisiana earlier and transferred it back to France in a secret agreement, but France was the country that formally sold Louisiana to the United States. The territory’s boundaries were also initially uncertain, creating later disputes with Spain and Britain.