The Treaty of Fontainebleau, signed on November 3, 1762, was a secret agreement of 1762 in which the Kingdom of France ceded Louisiana to Spain.
This agreement covered all of French Louisiana: the entire valley of the Mississippi River, from the Appalachians to the Rockies.
The Treaty of Paris, made between France and Great Britain following the Seven Years' War, divided Louisiana at the Mississippi.
O'Reilly made good Spain's title by occupancy by taking formal possession in 1769 and raising the Spanish flag.
When Great Britain returned Florida to Spain in 1783, after the American Revolutionary War, Spanish territory completely encircled the Gulf of Mexico and stretched from Florida west to the Pacific Ocean, and north to Canada west of the Mississippi River.