The significance of the Louisiana Purchase was that it allowed the United States to continue its westward expansion, it more than doubled the size of the U.S. and it kept the U.S. from going to war with France. It was a shrewd business move on Napoleon's part because he needed money for his war with England, and he knew he couldn't keep the Americans out of New Orleans without a fight, which he didn't have the military to cover.
The territory that President Thomas Jefferson purchased stretched from the Mississippi River to the Rocky Mountains, encompassing all or parts of 15 present-day U.S. states and two Canadian provinces. It gave the U.S. access to the port in New Orleans, which was necessary for trade since the new American settlements west of the Appalachian Mountains depended on it for their goods. Napoleon's asking price was $15 million, which came out to four cents an acre.