France was willing to sell the Louisiana Territory because Napoleon decided that it was too expensive to try to hold such a vast amount of land in the western hemisphere, and he needed the money for an upcoming war with England. Other factors were a French military failure in Haiti, the weakness of the French navy and the French inability to control the American pioneer movement heading west.
New Orleans, at the mouth of the Mississippi River, was vital for American trading and shipping. Thomas Jefferson sent envoys to France to negotiate the purchase of New Orleans and the land east of the Mississippi only. In April of 1803, Napoleon offered the United States the entire Louisiana Territory, which consisted of about 828,000 square miles of land.
The Louisiana Purchase was one of the most important acts of Thomas Jefferson's presidency. The total negotiated price was $15 million, consisting of $2 million in cash up front, $11.25 million over 20 years and the rescinding of a $3.75 million French debt to the United States. The price figured out to less than 3 cents an acre for the land. The purchase doubled the size of the United States. From it were carved eight complete new states and most of the territory of five more states.