What was the Louisiana Purchase?

In 1803 the United States purchased the Louisiana Territory from France, roughly 828,000 square miles stretching from the Mississippi River to the Rocky Mountains and from the Gulf of Mexico to present-day Canada, for about 15 million dollars including assumed debts. It doubled the nation's size at a price often calculated at around three cents per acre. Jefferson had sent envoys to negotiate only for New Orleans and access to the Mississippi, which was commercially essential to western farmers, and Napoleon unexpectedly offered the entire territory.

Napoleon's reasons were strategic. France had lost an enormous army to combat and yellow fever attempting to suppress the Haitian Revolution, which ended French ambitions for an American empire, and war with Britain was resuming, making a distant territory both indefensible and a useful source of cash. Jefferson, a strict constructionist who believed the Constitution granted only enumerated powers, could find no explicit authority for acquiring territory and privately doubted the purchase was constitutional. He proceeded anyway and let the Senate ratify it, which is an early and consequential example of practical necessity shaping constitutional interpretation.

The consequences were vast and not uniformly celebrated. It opened the interior to American settlement, prompted the Lewis and Clark expedition, and eventually formed all or part of fifteen states. It also meant that the land's existing inhabitants, numerous Native nations who were neither party to nor bound by the transaction, were subjected to displacement and dispossession over the following decades, culminating in forced removals. And the question of whether slavery would extend into the new territory drove the Missouri Compromise and the sectional conflicts that led to civil war.