In the late 18th century, the region west of the Mississippi river was under the possession of France. The mostly unknown and thinly populated territory was ceded to Spain from France in 1762 and then was transferred back to France in 1800, under the Treaty of San Ildefonso.
During those years, the city of New Orleans, at the mouth of the Mississippi River, has become an important port for shipping goods to and from the parts of the US west of the Appalachian Mountains.
With the port becoming more and more important to American trade interests, the Jefferson administration came to the conclusion that it would be in the best interest of the young American nation to purchase the city of New Orleans and the nearby portions of Louisiana east of the Mississippi.
In 1801 Jefferson sent Robert R. Livingston to Paris to negotiate such a purchase, however the French were not, at first, receptive.