As ruler of France, Napoleon Bonaparte engaged his country in his desire for empire. So, when Spain signed a secret treaty in 1801 returning the Louisiana territory to France, many of the American settlers going West became worried that the Mississippi River and the strategic port of New Orleans at the mouth of the Mississippi might be closed to them. In addition, officials of the United States were concerned about Bonaparte, and how he might seek to dominate the port at the Gulf of Mexico and access to the Mississippi. Consequently, President Thomas Jefferson worried that America could only defend itself if it were aligned with Great Britain.
Not wishing to again be under the influence by the British, Jefferson sent future president James Monroe to France, to aid U.S. minister Robert Livingston. Surprisingly, in mid-April 1803, France not only offered to sell the port of New Orleans, but also all their territory in America. It is suspected that the heavy financial toll on France of empire-building, quelling a slave revolution in Haiti, and impending war with Great Britain led to France's offer to sell all their American holdings for the ridiculous price of only 5 cents per acre:
The U.S. paid 50 million francs ($11,250,000) plus cancellation of debts worth 18 million francs ($3,750,000), for a total sum of 15 million dollars (around 4 cents per acre) for the Louisiana territory ($236 million in 2013 dollars, less than 42 cents per acre).
With this purchase, the United States now had full possession of both the Mississippi River and the Port of New Orleans, and the middle of the country now belonged entirely to the United States. In fact, 15 states were formed from this great tract of land.