The Louisiana Purchase was the 1803 acquisition that nearly doubled the size of the United States.
The United States agreed to buy the Louisiana Territory from France for $15 million. The treaty was signed on April 30, 1803, during Thomas Jefferson’s presidency, and the transfer formally began later that year.
The territory covered about 828,000 square miles, including land in or forming parts of 15 present-day U.S. states and two Canadian provinces. It stretched west of the Mississippi River and included the strategically important port of New Orleans.
Jefferson had initially focused on securing New Orleans and navigation rights on the Mississippi. France’s offer of the entire territory transformed the negotiations. The purchase expanded U.S. sovereignty westward, although its boundaries were disputed and the land was already home to many Native nations. The acquired region was later organized into territories and states, greatly shaping the country’s continental growth.