On 27 September 1821, the Army of the Three Guarantees entered Mexico City. Its columns carried the colors of a movement promising religion, independence and union. The entry marked the effective end of eleven years of war against Spanish colonial rule and the consummation of Mexican independence, although the formal Act of Independence would be issued the following day.
The scene was triumphant, but the settlement behind it was complicated. The final coalition joined former royalist officer Agustín de Iturbide with insurgent leader Vicente Guerrero. It achieved independence through compromise after a conflict that had begun with a popular revolt and passed through executions, guerrilla war, constitutional crisis and political realignment.
From the Cry of Dolores to a long war
The struggle began in September 1810 when Miguel Hidalgo y Costilla called for resistance in Dolores. The early insurgency mobilized enormous numbers but lacked stable organization. Royalist forces defeated its principal armies; Hidalgo and other leaders were captured and executed in 1811.
José María Morelos reorganized the movement, convened a congress and articulated an independent political program. He too was captured and executed, in 1815. Resistance survived in regional guerrilla campaigns, including those associated with Vicente Guerrero. By the end of the decade, neither simple royal restoration nor decisive insurgent victory had resolved New Spain’s future.
A revolution in Spain changes the equation
In 1820, a liberal revolution in Spain forced King Ferdinand VII to restore the Constitution of 1812. For conservative elites and clergy in New Spain, constitutional liberalism threatened established privileges. Independence, once associated with insurgent social revolution, became attractive to people who believed separation could preserve order, monarchy and the Catholic establishment.
Iturbide had fought for the royalist cause. Sent against Guerrero, he instead opened negotiations. Their political convergence did not erase their different histories, but it produced the alliance capable of ending the war.
The Plan of Iguala
On 24 February 1821, Iturbide proclaimed the Plan of Iguala. It rested on three guarantees: the Roman Catholic religion, Mexican independence and union among the inhabitants of the new state. It proposed a constitutional monarchy and offered the crown to Ferdinand VII or another European prince.
The Army of the Three Guarantees grew as military units and provincial leaders adhered to the plan. The movement promised continuity to institutions and protection to former opponents, which helped it attract support beyond the surviving insurgency.
Juan O’Donojú arrived as Spain’s senior political authority in New Spain in 1821. Recognizing the balance of power, he met Iturbide and signed the Treaties of Córdoba in August. The agreement accepted the main principles of the Plan of Iguala, though the Spanish government later rejected O’Donojú’s authority to recognize independence.
On the ground, however, Spanish colonial government was disintegrating. The remaining royal forces could not reverse the political and military coalition supporting separation. Mexico City prepared for the entry of the new army.
The entry on 27 September
The Army of the Three Guarantees marched into the capital in a carefully staged procession. Later paintings and prints turned the entry into a foundational national image. They should be read as commemorations rather than photographs: visual statements about unity and victory created after the event.
The date carried personal symbolism for Iturbide—it was his thirty-eighth birthday—but the event belonged to a much broader history. Insurgents, royalist converts, local communities, clergy, militias and civilian supporters had all shaped the outcome. The entrance closed the military phase in the capital while opening a difficult struggle over the nature of the new state.
On 28 September, the provisional governing junta issued the Act of Independence of the Mexican Empire. Independence did not immediately produce a stable republic. Iturbide was proclaimed emperor in 1822, faced opposition and abdicated in 1823. A federal republic followed in 1824.
Spain did not formally recognize Mexican independence until 1836, and Spanish forces held the fortress of San Juan de Ulúa off Veracruz until 1825. Nor did independence resolve deep inequalities created under colonial rule. Political conflict over federalism, centralism, church, army and regional power continued.
The Three Guarantees as a political bargain
The Plan of Iguala, proclaimed on 24 February 1821, supplied the coalition with its program and its name. Its three guarantees were Catholic religion, political independence and union among the inhabitants of New Spain. It proposed a constitutional monarchy and offered the crown first to Ferdinand VII or another European prince. The plan protected many existing institutions and social positions, helping former royalists embrace independence without accepting the more radical implications of the insurgency that had begun in 1810.
For Vicente Guerrero and other surviving insurgents, alliance with Iturbide created a path from regional resistance to national victory. For Iturbide and conservative supporters, independence promised control over Mexico’s political future after the liberal revolution of 1820 restored the Spanish Constitution and challenged established privileges. Their agreement did not erase old hostility or settle who would rule. It temporarily joined groups that had fought one another around a formula broad enough to defeat an exhausted viceregal order.
The colors associated with the Trigarante cause represented the guarantees, although their precise arrangement and later national meanings evolved. More important than the symbolism was the coalition’s momentum. Royalist units defected, cities accepted the plan and the balance of power shifted without a single final battlefield deciding the war.
Córdoba, authority and the last viceroyal government
Juan O’Donojú arrived in 1821 as Spain’s senior political authority in New Spain, though he carried the title jefe político superior rather than the traditional office of viceroy. Confronted with the collapse of royal control, he met Iturbide at Córdoba. On 24 August they signed a treaty recognizing the core of the Plan of Iguala and envisioning an independent Mexican empire.
O’Donojú did not have authority from Madrid to surrender sovereignty, and the Spanish government later rejected the Treaty of Córdoba. On the ground, however, his agreement helped arrange the peaceful transfer of Mexico City. Francisco Novella, commanding the remaining royalist position in the capital, eventually accepted the new situation after negotiations that included O’Donojú and representatives of the independence movement.
This legal ambiguity is one reason the September dates must be stated carefully. The Trigarante army’s entry on the 27th consummated independence in political and military terms. The Act of Independence, issued by the new Sovereign Provisional Governing Junta on 28 September, declared it in a formal document. Spain did not recognize Mexican independence until 1836.
The capital as a stage for a new order
The 27 September procession transformed a coalition into a public government. Troops entered a capital that had been the center of viceregal authority for three centuries. The army’s disciplined appearance, banners and route through the city communicated control as much as celebration. A successful entrance reassured supporters, confronted opponents with a fait accompli and placed Iturbide visibly at the center of the victory.
The triumph also concealed unresolved questions. The Plan of Iguala promised union, but independence did not end inequalities of wealth, region or race. The monarchy it proposed soon became Iturbide’s own empire. He was proclaimed emperor in 1822, clashed with the constituent congress and abdicated in 1823. A federal republic followed under the Constitution of 1824. The speed of those changes shows that agreement on separation from Spain was not agreement on Mexico’s political form.
Nor did the parade belong to one man alone. The final settlement rested on insurgents who had sustained resistance after the executions of Hidalgo and Morelos, on communities that supplied or sheltered them, on royalist defections and on an Atlantic constitutional crisis. Later national memory alternately elevated and condemned Iturbide, while Guerrero’s role became central to other narratives of independence.
Seen in that wider frame, 27 September was both an ending and an opening. It closed the military struggle for colonial rule in the capital. It began the harder contest over who would define citizenship, sovereignty and authority in the new state.
Mexico commemorates both the beginning and the consummation of independence. The famous national celebration centers on 16 September and Hidalgo’s 1810 uprising. The events of 27 and 28 September 1821 mark the war’s political conclusion and the creation of a sovereign state.
The distinction is important. Nations rarely emerge in a single moment. Mexico’s independence unfolded through rebellion, repression, constitutional change, alliance and negotiation. The army’s entry into Mexico City made that long process visible in the streets of the capital.
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The Plan of Iguala’s three guarantees were a political formula broad enough to join former enemies. “Religion” protected the exclusive position of Roman Catholicism. “Independence” ended subordination to Spain. “Union” promised equality and cooperation between American-born and European-born residents of New Spain.
The formula reduced fears among elites and royalist officers, but it did not answer every social demand raised since 1810. Indigenous communities, mixed-race populations, rural insurgents, merchants, clergy and military leaders did not all understand independence in the same way. The coalition succeeded because it postponed some conflicts as much as because it resolved others.
National memory has often centered Iturbide’s role in the final settlement, while Guerrero embodied continuity with the insurgency. Their alliance is traditionally associated with the “Embrace of Acatempan,” though details of the meeting are debated. Surviving correspondence more securely documents negotiation and convergence.
The partnership was politically powerful because each man brought a different source of legitimacy. Guerrero represented armed resistance that had survived repeated royalist campaigns. Iturbide could attract conservative institutions and military units that might otherwise oppose independence. The Army of the Three Guarantees joined those constituencies under a single public program.
The Treaties of Córdoba adapted the Plan of Iguala and recorded O’Donojú’s acceptance of Mexican independence. Yet O’Donojú did not possess authority to make Spain recognize the loss of the colony, and Madrid rejected the agreement. Independence therefore rested first on political and military reality in Mexico rather than immediate international recognition.
The remaining Spanish position at San Juan de Ulúa illustrates the incomplete transition. The fortress held out after the capital changed hands. Sovereignty was declared in 1821, consolidated territorially over time and recognized by Spain only in 1836.
The offer of a Mexican throne to a European prince failed. Iturbide became Emperor Agustín I in 1822. Relations with the congress deteriorated, opposition grew, and he abdicated in 1823. Mexico adopted a federal republican constitution in 1824.
That rapid change does not make the independence entry meaningless. It shows that agreement on separation from Spain did not produce agreement on government. Monarchy versus republic, federal versus central authority, the privileges of church and army, and the balance between regions remained open questions.
Mexico’s principal Independence Day commemorates 16 September 1810, not the capital entry of 1821. That choice emphasizes the uprising associated with Hidalgo and the beginning of popular struggle. The date 27 September marks consummation: the moment a victorious coalition occupied the center of colonial government.
Both dates are necessary to understand independence. One begins a revolutionary war; the other concludes it politically in the capital. The eleven years between them warn against compressing national independence into a single hero or ceremony.
The best-known depictions of the Trigarante entry were created after 1821. They arrange generals, flags and spectators into a harmonious founding scene. Such images are valuable evidence for later memory, but they are not direct visual recordings.
That distinction is why the captions in this article identify later paintings and lithographs as commemorative. They show how Mexicans represented the birth of the nation and the place assigned to Iturbide’s army. Documentary claims about the procession itself come from texts, official records and historically grounded institutional accounts.
