Spanish attempts to reconquer Mexico
Mexican independence was officially achieved on September 27, 1821, under the Treaty of Córdoba. Spain did not recognize the treaties, arguing that the viceroy Juan O'Donojú had no authority to recognize the independence of any overseas province. This situation was dangerous to the newly acquired independent status of the nation, which had not yet been recognized by any of the European powers that could support it, and the threat of Spanish reconquest was a constant worry to the leaders of the nascent regime. On May 13, 1822 decrees were issued by the government to imprison anyone who conspired against Mexico's independence.
Mexican War of Independence
The reinstatement of the liberal Constitution of Cadiz in 1820 caused a change of mind among the elite groups who had supported Spanish rule. Monarchist Creoles affected by the constitution decided to support the independence of New Spain; they sought an alliance with the former insurgent resistance. Agustín de Iturbide led the military arm of the conspirators and in early 1821 he met Vicente Guerrero. Both proclaimed the Plan of Iguala, which called for the union of all insurgent factions and was supported by both the aristocracy and clergy of New Spain. It called for a monarchy in an independent Mexico. Finally, the independence of Mexico was achieved on September 27, 1821.