1519–1521: The Spanish Conquest of the Aztec Empire

In 1519, central Mexico was dominated by the Triple Alliance of Tenochtitlan, Texcoco and Tlacopan, established in 1428. The Mexica capital, Tenochtitlan, stood on islands in Lake Texcoco and governed through tribute, warfare and alliances rather than uniform territorial administration. Subject communities delivered textiles, food, cacao, feathers and captives; resentment created openings that the invaders exploited.

Population estimates remain disputed. Archaeologist Eduardo Matos Moctezuma has commonly placed Tenochtitlan at roughly 200,000 inhabitants around 1519, while other modern estimates range from about 150,000 to 300,000. Historical demographer Woodrow Borah estimated approximately 25.2 million people in central Mexico in 1519; later scholars, including Robert McCaa, have stressed the uncertainty and wide variation among reconstructions.

Mesoamerica contained competing states, including Tlaxcala, which had resisted Mexica encirclement. The Totonacs of Cempoala also faced imperial tribute demands. These societies were not passive auxiliaries: their rulers pursued their own survival and regional power.

The conquest was a Spanish-Indigenous war against Mexica imperial power, followed by Spanish domination of victors, enemies and bystanders alike.

Cortés sailed from Cuba in 1519 under an expedition initially authorized by Governor Diego Velázquez de Cuéllar, then rejected Velázquez’s control. After founding Veracruz, he scuttled or disabled most of his ships and advanced inland. Fighting with Tlaxcalans in September 1519 gave way to an alliance indispensable to Spanish survival.

Date	Event	Consequence
February 1519	Cortés leaves Cuba with 11 ships and about 500–600 Spaniards, according to contemporary and later narrative estimates	He begins an unauthorized bid for independent command
March 1519	Spanish forces defeat Maya fighters at Centla	Malintzin enters Cortés’s party and becomes translator and political intermediary
April 1519	Cortés lands near present-day Veracruz	Totonac contacts expose opposition to Mexica tribute rule
September 1519	Spaniards fight, then ally with Tlaxcala	Thousands of Indigenous troops and essential supplies reinforce the expedition
October 1519	Spanish and allied troops massacre inhabitants at Cholula	Terror clears the route toward Tenochtitlan; reported deaths range from about 3,000 in Cortés’s 1520 account to 6,000 in later traditions
8 November 1519	Cortés enters Tenochtitlan and meets Moctezuma II	Spaniards soon hold the ruler under coercive custody
May 1520	Pedro de Alvarado orders the Tóxcatl festival massacre	Mexica resistance erupts across the capital
30 June–1 July 1520	Spaniards and allies flee during La Noche Triste	Contemporary claims vary; several hundred Spaniards and perhaps thousands of allies die
September–November 1520	Smallpox spreads through the Basin of Mexico	The epidemic kills many inhabitants, including ruler Cuitláhuac
28 April 1521	Cortés launches 13 brigantines on Lake Texcoco	Spanish-led forces tighten the naval blockade
26 May–13 August 1521	Tenochtitlan is besieged for 80 days	Hunger, disease and assault devastate the city
13 August 1521	Cuauhtémoc is captured	Organized defense of Tenochtitlan collapses

“We attacked them in the city all day long, and drove them from many of their strong positions.” — Hernán Cortés, 1522, Third Letter to Charles V

The quotation comes from a self-justifying report written to secure royal recognition. Indigenous-language accounts preserved by Bernardino de Sahagún’s collaborators describe thirst, corpses and civilians crushed during the siege.

No reliable ledger records the conquest’s total dead. Cortés began in 1519 with roughly 500–600 Spaniards, 16 horses and 10 cannon in commonly cited reconstructions based on sixteenth-century accounts. By the siege in 1521, Spanish forces numbered roughly 900, while allied Indigenous forces fluctuated in the tens of thousands; some campaign claims rise above 100,000, but they are not independently verifiable.

Cortés claimed in 1522 that more than 40,000 people were killed or captured on the final day, 13 August 1521, and that over 67,000 had died in earlier fighting; historians treat these figures cautiously because they served a propagandistic royal report. Bernardino de Sahagún’s Nahua testimony records mass death without producing a dependable total. Modern summaries often suggest tens of thousands died during the 1521 siege from combat, starvation and disease.

Smallpox, introduced in 1520, was decisive but not solitary: warfare, displacement, famine and later epidemics compounded mortality. Borah and Sherburne Cook estimated central Mexico’s population fell from 25.2 million in 1519 to 6.3 million in 1548 and about 1.1 million in 1605. Those 1519, 1548 and 1605 estimates are influential but contested; alternative starting estimates are substantially lower.

The fall of Tenochtitlan allowed Cortés to establish a Spanish capital, Mexico City, over its ruins in 1521. Charles V appointed him governor and captain general of New Spain in 1522. The Crown created the Viceroyalty of New Spain in 1535 under Antonio de Mendoza, curbing conquistador autonomy while institutionalizing colonial rule.

Conquerors received encomiendas: grants to extract tribute and labor from designated Indigenous communities, formally coupled with Christian instruction. Enslavement also continued, especially through classifications of captives as rebels. The Crown’s New Laws of 1542 attempted to restrict Indigenous enslavement and hereditary encomiendas, but colonists resisted and exploitation persisted through tribute, repartimiento labor and estate expansion.

Franciscan missionaries known as the Twelve arrived in 1524. Churches rose on or beside sacred sites; manuscripts and ritual objects were destroyed, while Indigenous communities preserved and reshaped languages, histories and religious practices. Conquest spread far beyond the capital through campaigns against regions that had never belonged to the Triple Alliance. This longer colonial violence belongs in the archive’s /atrocities record and continental /timeline.

Older imperial histories portrayed Cortés and a few hundred Spaniards as defeating millions through superior civilization. That story erases Tlaxcalan, Texcocan, Totonac and other Indigenous armies. It also turns epidemic disease into an absolution, ignoring deliberate massacres at Cholula in 1519 and Tóxcatl in 1520, hostage-taking, starvation tactics and colonial exploitation.

Malintzin has alternately been condemned as “La Malinche” or recognized as an enslaved Nahua woman whose interpreting shaped negotiations under coercive conditions. Tlaxcalans are likewise miscast as timeless traitors to a Mexican nation that did not exist in 1519. They allied against a regional imperial enemy; Spain later subordinated them despite limited privileges.

Public commemorations remain politically charged. Mexico marked 13 August 2021 as 500 years of “Indigenous resistance,” rejecting triumphalist conquest language. Monuments to Cortés and Columbus, museum labels and school curricula still determine whose agency and suffering enter public memory.

13 August 1521 was not the disappearance of Indigenous peoples. It was the military destruction of a capital and the beginning of a colonial regime resisted for centuries.

• Encyclopaedia Britannica: Hernán Cortés
• Fordham University: Cortés, Second Letter to Charles V
• World History Encyclopedia: Fall of Tenochtitlan
• Cambridge University Press: The Cambridge History of the Native Peoples of the Americas, Volume II
• University of California Press: The Population of the Valley of Mexico