In 1502 Moctezuma II, the last Mexica to rule before the arrival of the Spaniards, was named tlatoani. Moctezuma inherited a strained empire. His predecessors had expanded the empire’s reach from the Caribbean coast to the Pacific. At the margins of the empire the Aztecs encountered peoples who were seminomadic or who, like the Maya, abandoned their cities to resist conquest. An empire that had expanded rapidly through conquest found itself with little room to grow.

Aztec leaders had sought targets for conquest that were easy to overpower or were strategic for trade, or that possessed resources or produced goods that made for valuable tribute. This created an empire riddled with independent enclaves that had resisted conquest. The most powerful of these was Tlaxcala, at the edge of the Valley of Mexico. In addition, even those areas nominally under Aztec rule retained local leadership and saw themselves as subjected peoples, not as Aztecs.

Finally, the costs of expanding and sustaining the empire had become onerous. Generations of social mobility through distinction in combat had produced a bloated nobility both exempt from and sustained by tribute. Tenochtitlan became dependent on tributary maize in order to feed itself. Materially, the lack of new peoples to conquer meant the empire had little promise of increased prosperity. Spiritually, the dwindling flow of sacrificial victims meant the Mexica might be losing the great cosmic struggle to keep creation from ending.

Faced with these challenges, Moctezuma II reformed the empire. He reduced the privileges (and thus the costs to the empire) of the lesser nobility and narrowed the pathways of social mobility. The austerity he imposed in the imperial capital caused unrest. He also pressed the consolidation of territory by seeking to conquer the autonomous enclaves left by his predecessors. As Moctezuma targeted these enclaves, their ability to resist sapped Mexica resources and strained their morale without producing a corresponding reward for the empire in sacrifice or tribute.

By the time he reached the gates of Tenochtitlan in 1519, the Spanish conquistador Hernán Cortés had forged alliances with foes of the Aztec Empire, particularly Tlaxcala, which had so ably resisted conquest. The Tlaxcalans saw in the foreigners an opportunity that could aid their struggle against the Mexica and formed an alliance with the Spanish. Cortés’s band of six hundred Spaniards arrived in Tenochtitlan accompanied by tens of thousands of Tlaxcalan soldiers.

Whatever Moctezuma made of the strangers, he received them as guests, probably because he sought to understand the nature of this encounter and its significance for his empire. Perhaps Moctezuma hesitated, losing the opportunity to act against them. Perhaps he concluded that he had no chance of defeating them, since at that moment most of the men he could count on in battle were tending to their crops and the capital had been so riddled with division and resentment of his reforms that he was powerless to act.

Either way, Cortés and his men managed the encounter skillfully and succeeded in taking Moctezuma prisoner. When the residents of Tenochtitlan rose up to expel the Spaniards, Moctezuma was killed, either at the hands of the Spaniards or by his own subjects, depending on the account. Though the Spaniards were cast out of the city, they left an unwelcome guest, smallpox. The first epidemic of the disease swept through the city in 1520, killing Moctezuma’s successor, Cuitlahuac, within a matter of months. Cuauhtemoc, the last tlatoani of the Mexica, was named that same year.

The Aztec Empire and the Mexica people were not defeated by technology, cultural superiority, or a belief that the Europeans were gods. Instead the Mexica suffered a political defeat: they fell because of ruptures in their leadership due to the death of Moctezuma and his successor, as well as the willingness of allies and enemies alike to join with the Spaniards against them when they perceived an opportunity.