The Louisiana Purchase was the 1803 land deal that greatly expanded the territory of the United States.
The United States purchased the territory from France for $15 million. The agreement was completed during Thomas Jefferson’s presidency and transferred roughly 828,000 square miles of land west of the Mississippi River to the United States.
The purchase effectively doubled the country’s size, although its exact boundaries and the legal status of many inhabitants required later clarification. The territory included land drained by the Mississippi and Missouri river systems and eventually became all or parts of fifteen U.S. states.
The deal is sometimes confused with the Alaska Purchase of 1867, which transferred Alaska from Russia, or the Gadsden Purchase of 1853, which added land in the present-day American Southwest. The Louisiana Purchase was much earlier and far larger.