Therefore, the Mexican Congress elected a Mexican monarch the following year. Iturbide was proclaimed emperor of Mexico on May 18, 1822. The monarchy lasted three years, and after the republican revolution of Casa Mata, the Congress no longer considered the Plan of Iguala or Treaty of Córdoba in effect. See also Adams–Onís Treaty — 1819 U.S.—Spain treaty regarding border locations List of treaties References External links Treaty of Córdoba and other relevant documents (English & Spanish versions) Cordoba . Cordoba Cordoba 1821 in Mexico 1821 in New Spain 1821 in Spain Cordoba Cordoba, Treaty of 1821 in Alta California 1820s in Mexico Mexico–Spain relations Córdoba, Veracruz August 1821 events