The Triple Alliance (1428-1521) was a military and political pact among three city-states who shared lands in the Basin of Mexico (what is essentially Mexico City today): Tenochtitlan, settled by the Mexica/Aztec; Texcoco, home of the Acolhua; and Tlacopan, home of the Tepaneca. That accord formed the basis of what was to become the Aztec Empire that ruled Central Mexico and eventually most of Mesoamerica when the Spanish arrived at the very end of the Postclassic period.

We know quite a bit about the Aztec Triple Alliance because histories were compiled at the time of the Spanish conquest in 1519. Many of the native historical traditions collected by the Spanish or preserved in the towns contain detailed information about the dynastic leaders of the Triple Alliance, and economic, demographic, and social information comes from the archaeological record.

The Rise of the Triple Alliance

During the late Postclassic or Aztec Period (CE 1350-1520) in the Basin of Mexico, there was a rapid centralization of political authority. By 1350, the basin was divided into several small city-states (called Altepetl in the Nahuatl language), each of which was ruled by a petty king (Tlatoani). Each altepetl included an urban administrative center and a surrounding territory of dependent villages and hamlets.

Some of the city-state relationships were hostile and plagued by nearly constant wars. Others were friendlier but still competed with one another for local prominence. Alliances between them were built and sustained through a vital trade network and a commonly shared set of symbols and art styles.

By the late 14th century, two dominant confederations emerged. One was led by the Tepaneca on the western side of the Basin and the other by the Acolhua on the eastern side. In 1418, the Tepaneca based at Azcapotzalco came to control most of the Basin. Increased tribute demands and exploitation under the Azcapotzalco Tepaneca led to a revolt by the Mexica in 1428.

Expansion and the Aztec Empire

The 1428 revolt became a fierce battle for regional domination between Azcapotzalco and the combined forces from Tenochtitlan and Texcoco. After several victories, the ethnic Tepaneca city-state of Tlacopan joined them, and the combined forces overthrew Azcapotzalco. After that, the Triple Alliance moved quickly to subdue other city-states in the basin. The south was conquered by 1432, the west by 1435, and the east by 1440. Some longer holdouts in the basin include Chalco, conquered in 1465, and Tlatelolco in 1473.

These expansionist battles were not ethnically-based: the bitterest were waged against the related polities in the Puebla Valley. In most cases, the annexation of communities simply meant the establishment of an additional layer of leadership and a tribute system. However, in some cases such as the Otomi capital of Xaltocan, archaeological evidence indicates that the Triple Alliance replaced some of the population, perhaps because the elites and commoner people fled.

An Unequal Alliance

The three city-states sometimes operated independently and sometimes together. By 1431, each capital controlled certain city-states, with Tenochtitlan to the south, Texcoco to the northeast and Tlacopan to the northwest. Each of the partners was politically autonomous. Each ruler king acted as the head of a separate domain. But the three partners were not equals, a division that increased over the 90 years of the Aztec Empire.

The Triple Alliance divided booty recovered from their wars separately. 2/5 went to Tenochtitlan, 2/5 to Texcoco, and 1/5 (as the latecomer) to Tlacopan. Each leader of the alliance divided his resources among the ruler himself, his relatives, allied and dependent rulers, nobles, meritorious warriors, and to local community governments. Although Texcoco and Tenochtitlan began on a relatively equal footing, Tenochtitlan became preeminent in the military sphere, while Texcoco retained prominence in law, engineering, and the arts. Records do not include references to Tlacopan's specialties.

Benefits of the Triple Alliance

The Triple Alliance partners were a formidable military force, but they were also an economic force. Their strategy was to build on pre-existing trade relations, expanding them to new heights with state support. They also focused on urban development, dividing the areas into quarters and neighborhoods and encouraging an influx of immigrants into their capitals. They established political legitimacy and fostered social and political interactions through alliances and elite marriages within the three partners and throughout their empire.

Archaeologist Michael E. Smith argues that the economic system was taxation, and not tribute since there were regular, routinized payments to the Empire from the subject states. This guaranteed the three cities a consistent flow of products coming in from different environmental and cultural regions, increasing their power and prestige. They also provided a relatively stable political environment, where commerce and marketplaces could flourish.

Domination and Disintegration

The king of Tenochtitlán soon emerged as the supreme military commander of the alliance and made the final decision on all military actions. Eventually, Tenochtitlán began to erode the independence of first Tlacopán, then that of Texcoco. Of the two, Texcoco remained fairly powerful, appointing its colonial city-states and able to fend off Tenochtitlán's attempt to intervene in Texcocan dynastic succession right up until the Spanish conquest.

Most scholars believe that Tenochtitlán was dominant throughout most of the period, but the effective union of the alliance remained intact through political, social, and economic means. Each controlled their territorial domain as dependent city-states and their military forces. They shared the expansionist goals of the empire, and their highest-status individuals maintained individual sovereignty by inter-marriages, feasting, markets and tribute sharing across alliance borders.

But hostilities among the Triple Alliance persisted, and it was with the help of Texcoco's forces that Hernan Cortes was able to overthrow Tenochtitlán in 1591.