After the creation of the United States, the Americans controlled the area east of the Mississippi River and north of New Orleans. The main problem for the Americans was the free transit from the Mississippi to the sea. When the land was sparsely populated by American migrants, many Americans, including Jefferson, thought the area would be purchased „little by little.“ The risk that another power could emerge from a weakened Spain has necessitted a „profound revision“ of this policy.  New Orleans was already important for shipping agricultural goods to and from the U.S. territories west of the Appalachians. Pinckney`s contract, signed with Spain on October 27, 1795, gave American merchants a „deposit right“ in New Orleans and granted them the use of the port to store goods for export. The treaty also recognized the U.S. right to sail throughout Mississippi, which became vital to the growth of western territories` trade.  The territory of Louisiana has been divided into smaller parts for the administration, and the territories passed slavery laws similar to those of the Southern States, but which included provisions of the previous French and Spanish rule (for example, Spain had banned Indian slavery in 1769, but some slaves of mixed African-American descent were still held in St. Louis, Upper Louisiana when the United States took over).  In a freedom lawsuit from Missouri to the U.S. Supreme Court, Indian slavery finally ended in 1836.
 The institutionalization of slavery under U.S. law in the territory of Louisiana, half a century later, contributed to the American Civil War.  When states organized within the territory, the status of slavery in each state became a matter of conflict in Congress, because the southern states wanted slavery to be extended to the West and the northern states were equally strongly opposed to the accession of new states as „slave states“. The Missouri compromise of 1820 was a temporary solution. France presented New Orleans, the historic colonial capital, on December 20, 1803 to the Cabildo with a flag ceremony on the Plaza de Armas, now Jackson Square. Three weeks earlier, on 30 November 1803, Spanish officials had officially brought the colonial countries and their administration to France. Louisiana Purchase extended U.S. sovereignty over the Mississippi River, almost doubling the nominal size of the country.
The purchase included land from fifteen United States