What would you do if someone offered to sell you 828,000 square miles of land for less than 3 cents per acre? That is exactly what happened on April 30, 1803, when the United States signed a treaty with France. This deal, called the Louisiana Purchase, doubled the size of the country overnight. President Thomas Jefferson paid about $15 million, which works out to less than 3 cents per acre. The land stretched from the Mississippi River west to the Rocky Mountains. It reached from the Gulf of Mexico north to Canada. This territory included all or parts of 15 future states, including Louisiana, Arkansas, Missouri, Iowa, and Montana. The Mississippi River, which runs through the center of the purchase, was the most important waterway in North America. Farmers in the interior needed the river to ship their crops to market. The port city of New Orleans controls the river's mouth. It was especially valuable because whoever held it controlled trade across the continent's interior. Jefferson originally sent diplomats to France only to buy New Orleans. But Napoleon, who needed money for wars in Europe, offered to sell the entire territory. Jefferson jumped at the deal, even though many people questioned whether the Constitution allowed the president to buy land. The purchase changed America's geography forever.