Third Treaty of San Ildefonso

Background. France and Spain had been allies for much of the 18th century, but after Louis XVI's execution in 1793 Spain fought and lost the War of the Pyrenees. The 1796 Second Treaty of San Ildefonso brought Spain into the War of the Second Coalition against Britain, and the resulting blockade and financial strain—national debt rising eightfold between 1793 and 1798—left the Spanish government weakened.

Motives for the Exchange. After the November 1799 Coup of 18 Brumaire, Napoleon and Talleyrand pursued French overseas expansion, including restoring New France with Louisiana supplying Caribbean plantations. Spanish weakness, disputes with the U.S. over Mississippi navigation, and Talleyrand's claim that French Louisiana could shield Spanish South America made the retrocession attractive to both sides.

Terms and Conditions. Spain agreed in principle to cede Louisiana and six ships of the line—San Antonio, Intrepido, San Genaro, Atlante, Conquistador, and Infante Don Pelayo—in return for territories in Tuscany or other Italian provinces forming a rounded state. Urquijo insisted the handover occur only once France confirmed which Italian territories it would deliver, and the treaty reaffirmed the 1796 Franco-Spanish alliance.