The Louisiana Purchase nearly doubled the size of the United States

Sent to Paris merely to secure the port of New Orleans, American envoys Robert R. Livingston and James Monroe were stunned when Napoleon’s government offered to sell the entire Louisiana Territory instead. The treaty they signed was dated April 30, 1803.

For $15 million, the United States acquired roughly 828,000 square miles stretching from the Mississippi to the Rocky Mountains and from the Gulf coast toward Canada — land that would become all or part of 15 future states. The price worked out to about 4 cents an acre, and at a stroke the young republic nearly doubled in size.

Jefferson had quietly doubted he even had the constitutional power to buy it — then bought it anyway.

President Thomas Jefferson, a strict reader of the Constitution, fretted that it gave him no clear authority to purchase territory. He pressed ahead regardless, judging the bargain too vast to refuse, and the Senate ratified the deal that autumn.