What historical circumstances resulted in the Louisiana Purchase?

After the French-Indian War in 1763, France lost all of its North American holdings but maintained control of the island of Haiti.  After this war, Spain owned the land that would be known as the Louisiana Purchase.  During the Napoleonic War, France regained the territory and Napoleon intended on using the land as a granary to feed his army and the island of Haiti to provide sugar for trade.  In 1803, the slaves of Haiti overthrew their French masters and declared an independent nation.  Napoleon now saw the North American land as a hindrance, as it would be something else to defend against the British.  When Jefferson sent ambassadors to Napoleon to ask to use the port of New Orleans, Napoleon surprised them by offering to sell the entire territory, encompassing millions of acres.  Jefferson instructed his envoys to create a deal with the French, and the treaty was sent to Congress.  Congress, while upset that they were not consulted and that this massive land purchase was supposed to be outside the presidential realm of power, signed off on the popular land purchase, thus overnight more than doubling the size of the United States.