Origins
The Aztec people (more precisely Mexica — Aztec is a 19th-century European usage) entered the Valley of Mexico from the north in the late 13th century, settling on a swampy island in Lake Texcoco in 1325 and founding the city of Tenochtitlán. They were initially mercenary subordinates of the dominant Tepanec polity at Azcapotzalco. The Mexica overthrew their Tepanec overlords in 1428 in an alliance with the cities of Texcoco and Tlacopan, producing the Triple Alliance that would expand over the next century into the dominant tributary network of central Mexico.
The imperial system
The Aztec Empire was not a unified state in the modern sense. It was a tributary network: the three allied cities collected periodic tribute (food, textiles, military service, war captives for human sacrifice) from approximately 38 conquered provinces across central and southern Mexico. The conquered provinces retained local political institutions, languages, and religious practices, subject to Aztec military and fiscal supervision. The system was held together by the periodic punitive military campaigns the Aztec army conducted against tribute-resisters, by the ritual-religious centre of Tenochtitlán’s main temple complex, and by the calculated practice of human sacrifice that consumed war captives and provided regular ritual demonstration of Aztec military power.
The total population of the Aztec tributary network at peak (c. 1519) is estimated at approximately 5–6 million. The empire’s principal antagonists were the Purépecha of Michoacán (the only major Mesoamerican polity the Aztecs never defeated) and the Tlaxcalan confederation (a small independent state immediately east of the Aztec heartland).
Tenochtitlán itself was, in 1519, one of the largest cities in the world — approximately 200,000 inhabitants, built on an artificial island connected to the lakeshore by three large causeways, served by an extensive system of canals and aqueducts, dominated by the Templo Mayor pyramid. The first Spanish accounts treat the city as larger and more orderly than any city in contemporary Europe.
The Spanish conquest
The Aztec Empire was destroyed in a 26-month campaign (April 1519 – August 1521) by Hernán Cortés and a force that at its peak combined approximately 1,300 Spaniards with substantially larger contingents of Tlaxcalan and other indigenous allies (perhaps 80,000 to 200,000 indigenous troops by the final siege of Tenochtitlán).
Cortés landed near modern Veracruz in April 1519 with approximately 500 men, 100 sailors, 16 horses, and 14 small cannons. The Spanish force was numerically negligible by Aztec standards; its decisive advantages were steel weapons and armour, gunpowder weapons, horses, and (most importantly) the political-diplomatic exploitation of the substantial anti-Aztec sentiment among the empire’s subject peoples. The Tlaxcalan alliance (formalized after several weeks of initial fighting in September–October 1519) provided the substantial military manpower that made the campaign possible.
Cortés entered Tenochtitlán peacefully on 8 November 1519 and was received by the Aztec emperor Moctezuma II with considerable ceremony. The political situation deteriorated through the following months. Moctezuma was effectively imprisoned by Cortés. A Spanish detachment under Pedro de Alvarado massacred several hundred Aztec nobles during a religious festival in May 1520, producing a general uprising. The Spanish were driven out of Tenochtitlán on the night of 30 June – 1 July 1520 (the Noche Triste), losing approximately two-thirds of their force in the retreat. Moctezuma was killed in the fighting (probably by his own people; Spanish accounts attribute the death to a stoning).
Cortés rebuilt his forces in Tlaxcala, constructed a fleet of brigantines for use on the lake, and laid siege to Tenochtitlán from late May 1521. The siege lasted 75 days. Smallpox, introduced by an earlier Spanish landing party in late 1519, killed perhaps a quarter of the Tenochtitlán population during the siege and is conventionally cited as the single most consequential factor in the city’s defeat. The city fell on 13 August 1521. The last Aztec emperor Cuauhtémoc was captured fleeing across the lake; he was executed by Cortés in 1525 on a march into Honduras.
Consequences
Tenochtitlán was systematically demolished in the months following the fall and rebuilt as the Spanish colonial capital of Mexico City. The Aztec tributary structure was inherited by the Spanish crown and adapted as the encomienda and later the repartimiento labor systems that would extract Indigenous tribute and labour for Spanish settlers and the colonial state through the next three centuries.
The Aztec population collapsed by approximately 90% over the next 80 years, primarily from Old World epidemic disease (smallpox, measles, influenza, typhus). Recent demographic estimates put central Mexico’s indigenous population at approximately 25 million in 1519 and approximately 1.5 million by 1605. The collapse was the largest single demographic catastrophe in recorded human history.
The Mexica cultural and linguistic tradition survived under Spanish colonial rule. Modern Mexico’s official language is Spanish, but Nahuatl continues to be spoken by approximately 1.7 million people. Numerous Aztec institutions — the Templo Mayor (rediscovered in 1978 under central Mexico City), the surviving codices, the calendar systems, the religious-ritual practices documented by 16th-century Franciscan missionaries — survive as primary evidence of Mesoamerican civilization.
The Mexican national identity that emerged from the 19th-century independence movements incorporated the Aztec inheritance as a foundational symbolic element. The Mexican national flag’s central eagle on a cactus is the foundational myth of Tenochtitlán’s founding.