Old Heat and New Light on Spanish Diplomacy Regarding the Louisiana Purchase and the Defense ofNew Mexico, 1762-1819 .

This article focuses on Spanish diplomacy concerning the Louisiana Purchase and the defense of New Mexico from 1762 to 1819. It details Spain’s contention that the 1803 Louisiana Purchase between Napoleonic France and the United States was illegal, as France had not fulfilled prior treaty obligations with Spain, notably the Treaty of San Ildefonso (1800) and the Convention of Aranjuez (1802). Spain maintained historic claims to lands west of the Mississippi River, including the Trans-Mississippi West and the Great Plains, defended in part by New Mexico officials through expeditions and patrols against U.S. incursions. The 1817 Spanish draft of the Tratado de Amistad (Treaty of Friendship) and the 1819 Adams-Onís Treaty sought to resolve boundary disputes, ultimately ceding Florida to the U.S. and defining a western boundary line that limited Spanish territory but preserved claims from Texas to California. Despite these treaties, unresolved issues over western boundaries persisted until the U.S.-Mexico War and the Treaty of Guadalupe Hidalgo in 1848.