sign the treaty, but events on the ground saw Iturbide and the Army of Three Guarantees march into Mexico City in triumph on 27 September 1821. The next day, the Mexican independence was proclaimed in the Declaration of Independence of the Mexican Empire. The Plan of Iguala and the Treaty of Córdoba had rapidly brought about an alliance of insurgents and former royalists turned autonomists resulting in the rapid achievement of independence virtually without further military conflict. Once independence was achieved, the fissures between different interests rapidly re-emerged. Creation of the First Mexican Empire On 27 September 1821, the Army of the Three Guarantees entered Mexico City, and the following day Iturbide proclaimed the independence of the Mexican Empire, as New Spain was henceforth to be called. The Treaty of Córdoba was not ratified by the Spanish Cortes. Iturbide included a special clause in the treaty that left open the possibility for a criollo monarch to be appointed by a Mexican congress if no suitable member of the European royalty would accept the Mexican crown. Half of the new government employees appointed were Iturbide's followers. On the night of 18 May 1822, a mass demonstration led by the Regiment of Celaya, which Iturbide had commanded during the war, marched through the streets and demanded their commander-in-chief to accept the throne. The following day, the Congress declared Iturbide Emperor of Mexico. On 31 October 1822, Iturbide dissolved Congress and replaced it with a sympathetic junta. Spanish attempts to reconquer Mexico Despite the creation of the Mexican nation, the Spanish still managed to hold onto a port in Veracruz that Mexico did not get control of until 23 November 1825. Spanish attempts to re-establish control over Mexico culminated in the 1829 Battle of Tampico, during which a Spanish invasion force was surrounded in Tampico and forced to surrender. On 28 December 1836, Spain recognized the independence of Mexico under the Santa María–Calatrava Treaty, signed in Madrid by the Mexican Commissioner Miguel Santa María and the Spanish state minister José María Calatrava. Mexico was the first former colony whose independence was recognized by Spain; the second was Ecuador on 16 February 1840. Legacy In 1910, as part of the celebrations marking the centennial of the Hidalgo revolt of 1810, President Porfirio Díaz inaugurated the monument to Mexico's political separation from Spain, the Angel of Independence on Avenida Reforma. The creation of this architectural