Today is the 200th anniversary of the Louisiana Purchase:

On Dec. 20, 1803, ownership of more than 800,000 square miles - now part or all of 15 states - was formally transferred from France to the United States at ceremonies in New Orleans. President Jefferson had wanted to buy a portion of the land, which France had acquired from Spain in 1800, but wound up getting the whole parcel for $15 million

(from Associated Press, via Yahoo News).