<P> Throughout the second half of the 18th century, Louisiana was a pawn on the chessboard of European politics . It was controlled by the French, who had a few small settlements along the Mississippi and other main rivers . Following French defeat in the Seven Years' War, Spain gained control of the territory west of the Mississippi and the British the territory to the east of the river . </P> <P> Following the establishment of the United States, the Americans controlled the area east of the Mississippi and north of New Orleans . The main issue for the Americans was free transit of the Mississippi to the sea . As the lands were being gradually settled by a few American migrants, many Americans, including Jefferson, assumed that the territory would be acquired "piece by piece ." The risk of another power taking it from a weakened Spain made a "profound reconsideration" of this policy necessary . New Orleans was already important for shipping agricultural goods to and from the areas of the United States west of the Appalachian Mountains . Pinckney's Treaty, signed with Spain on October 27, 1795, gave American merchants "right of deposit" in New Orleans, granting them use of the port to store goods for export . Americans used this right to transport products such as flour, tobacco, pork, bacon, lard, feathers, cider, butter, and cheese . The treaty also recognized American rights to navigate the entire Mississippi, which had become vital to the growing trade of the western territories . </P> <P> In 1798, Spain revoked the treaty allowing American use of New Orleans, greatly upsetting Americans . In 1801, Spanish Governor Don Juan Manuel de Salcedo took over from the Marquess of Casa Calvo, and restored the American right to deposit goods . However, in 1800 Spain had ceded the Louisiana territory back to France as part of Napoleon's secret Third Treaty of San Ildefonso . The territory nominally remained under Spanish control, until a transfer of power to France on 30 November 1803, just three weeks before the formal cession of the territory to the United States on 20 December 1803 . A further ceremony was held in St. Louis a few months later partially due to winter conditions impeding the arrival of news, Upper Louisiana, regarding the New Orleans formalities . The 9--10 March 1804 event is remembered as Three Flags Day . </P> <P> James Monroe and Robert R. Livingston had traveled to Paris to negotiate the purchase of New Orleans in January 1803 . Their instructions were to negotiate or purchase control of New Orleans and its environs; they did not anticipate the much larger acquisition which would follow . </P>

When did louisiana become a part of the united states