<P> After 1810 the independence movement went through several stages, as leaders were imprisoned or executed by forces loyal to Spain . At first they recognized the sovereignty of Ferdinand VII over Spain and its colonies, but later the leaders took more radical positions, including such issues of social order as the abolition of slavery . Secular priest José María Morelos called the separatist provinces to form the Congress of Chilpancingo, which gave the insurgency its own legal framework . After the defeat of Morelos, the movement survived as a guerrilla war under the leadership of Vicente Guerrero . By 1820, the few rebel groups survived most notably in the Sierra Madre del Sur and Veracruz . </P> <P> 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 monarchy in an independent Mexico . Finally, the independence of Mexico was achieved on September 27, 1821 . </P> <P> After that, the mainland of New Spain was organized as the Mexican Empire . This ephemeral Catholic monarchy changed to a federal republic in 1823, due to internal conflicts and the separation of Central America from Mexico . </P> <P> After some Spanish reconquest attempts, including the expedition of Isidro Barradas in 1829, Spain under the rule of Isabella II recognized the independence of Mexico in 1836 . </P>

Who took the first step toward independence in mexico