Marc h 10: The Louisiana Territoy is transferred from France to the United States of America trough a formal ceremony in 1804.

The modern United States, with Louisiana Purchase overlay (in green)

While Napoleon I was focused on Europe a slave revolt broke up in Haiti. The United States President Thomas Jefferson was interested in acquiring New Orleans and its environs, but Government authorities were dumbfounded when the vastly larger territory was offered.

Ceremony at Place d’Armes, New Orleansmaking transfer of Louisiana to the United States, march 10 1804, as depicted by Thure de Thulstrup.

France had controlled the Louisiana Territory since 1699 until 1762 when it was transferred to Spain. Napoleón recovered the lands in North America in 1800, but his hostilities with Great Britain needed all possible resources and concentration.

http://www.umsl.edu/library/merc/exhibits/lewis_and_clark_maps/Louisiana_Purchase_main.htm 

There was domestic opposition in the United States about the Louisiana Purchase arguing unconstitutionality. President Thomas Jefferson took advantage of such a great opportunity and bought the whole territory for only US$15 million.