Spain ceded ownership of the Louisiana territory in 1800 to the more predominant France. Jefferson was greatly concerned that Napoleon's broad interests in the vast territory would threaten the security of the continent and Mississippi River shipping. He wrote that the cession "works most sorely on the U.S. It completely reverses all the political relations of the U.S."[195] In 1802, he instructed James Monroe and Robert R. Livingston to negotiate with Napoleon to purchase New Orleans and adjacent coastal areas from France.[196] In early 1803, Jefferson offered Napoleon nearly $10 million for 40,000 square miles (100,000 square kilometers) of tropical territory.[197]
Napoleon realized that French military control was impractical over such a vast remote territory, and he was in dire need of funds for his wars on the home front. In early April 1803, he unexpectedly made negotiators a counter-offer to sell 827,987 square miles (2,144,480 square kilometers) of French territory for $15 million, doubling the size of the United States.[197] U.S. negotiators seized this unique opportunity and accepted the offer and signed the treaty on April 30, 1803.[177] Word of the unexpected purchase did not reach Jefferson until July 3, 1803.