The Louisiana Purchase was the 1803 land deal that nearly doubled the size of the United States.
The United States acquired the territory from France for $15 million, or about three cents per acre according to the commonly cited calculation. The agreement was signed on April 30, 1803, and the transfer was completed later that year. The territory covered roughly 828,000 square miles west of the Mississippi River.
President Thomas Jefferson authorized the purchase, even though the Constitution did not explicitly describe a presidential power to buy territory. The deal secured American access to the port of New Orleans and the Mississippi River, both vital to western farmers and traders.
The purchase did not create all the modern states immediately. Its boundaries and governance developed over time, and the territory was later divided into multiple states and territories. It also displaced Indigenous nations and intensified disputes over slavery’s expansion.