In 1808, when news arrived in New Spain of Napoleon’s invasion of the Iberian Peninsula and the forced abdications of Spanish kings Charles IV and Ferdinand VII, the Mexico City council recalled a royal decree that had originally united New Spain with the Crown of Castile, along with Charles V’s promise never to sell or cede the territory to any other power.

City officials declared the royal abdications and the installation of Joseph Bonaparte on the Spanish throne invalid. Starting in 1809, secret revolutionary cells began forming across New Spain—especially in the Bajío region—working toward autonomy and, eventually, full independence.

The fight for freedom unfolded in four major stages:

• The broad initial uprising led by Miguel Hidalgo (1810–1811);
• The most intense phase under leaders like Ignacio López Rayón and José María Morelos (1811–1815);
• A period of decline and fragmentation with figures like Guadalupe Victoria, Manuel Mier y Terán, and Xavier Mina (1815–1819);
• The final chapter of independence in 1821, when insurgents and royalists united in the "Army of the Three Guarantees" under Agustín de Iturbide and Vicente Guerrero. The people rallied behind the "Plan of Iguala" and the "Treaties of Córdoba", which marked the birth of Mexico as a sovereign nation.