New France
In 1763, France had ceded the rest of New France, except the islands of Saint Pierre and Miquelon, to Great Britain and Spain at the Treaty of Paris, which ended the Seven Years' War (known as the French and Indian War in North America and especially the United States). Britain received Canada, Acadia, and the parts of French Louisiana which lay east of the Mississippi Riverexcept for the Île d'Orléans, which was granted to Spain, along with the territory to the westthe larger portion of Louisiana.
Three Flags Day
France had ruled Louisiana from its founding until the Treaty of Paris (1763) which ended the Seven Years' War (whose North American phase was the French and Indian War), in which treaty Spain received the French land west of the Mississippi River (the "right bank" going downstream) plus New Orleans, and Great Britain received the French lands east of the River (the "left bank") -- which included what had previously been called the Illinois Country or "Upper Louisiana".