The Treaty of Paris, made between France and Great Britain following the Seven Years' War, divided Louisiana at the Mississippi. The eastern half was ceded to Britain, and the western half and New Orleans were nominally retained by France. Spain did not contest Britain's control of eastern Louisiana, as it already knew that it would rule in western Louisiana. Also, under the Treaty of Paris, Spain had ceded Florida to Britain for which western Louisiana was its compensation.
https://en.wikipedia.org/wiki/Treaty_of_Fontainebleau_(1762)