Aztec Triple Alliance (1428): How the Aztec Empire Was Born

The Aztec Triple Alliance was the union of three city-states in the Valley of Mexico, Tenochtitlan, Texcoco and Tlacopan, formed around 1428 after they overthrew the dominant Tepanec state of Azcapotzalco. The alliance became the political core of the Aztec Empire, which by 1519 collected tribute from much of central and southern Mexico. Its creation marked the moment when the Mexica of Tenochtitlan rose from subordinate mercenaries to masters of Mesoamerica’s largest state.

Background: the Tepanec empire

In the early 15th century the Valley of Mexico was dominated by Azcapotzalco, the capital of the Tepanecs on the western shore of Lake Texcoco. Under its long-reigning king Tezozomoc, who ruled from the later 14th century until 1426, Azcapotzalco built a regional empire, forcing many lakeshore cities to pay tribute.

The Mexica of Tenochtitlan, whose island city had been founded in the 14th century as recounted in the founding of Tenochtitlan, were among Tezozomoc’s most useful subjects. They fought as his mercenaries and shared in some conquests. Their rulers married into Tepanec royalty, and Tenochtitlan’s king Chimalpopoca was Tezozomoc’s grandson.

Azcapotzalco’s main rival was Texcoco, the leading city of the Acolhua on the eastern shore. In 1418 Tepanec forces defeated Texcoco and killed its ruler, Ixtlilxochitl. His young son Nezahualcoyotl escaped and spent the following years as a fugitive and exile, as described in Nezahualcoyotl, poet-king of Texcoco.

The Tepanec succession crisis

Tezozomoc died in 1426. His son Maxtla pushed aside the designated heir and seized the throne. Maxtla was hostile to Tenochtitlan, whose rulers had supported his rival.

Within a short time Chimalpopoca of Tenochtitlan died, probably killed on Maxtla’s orders around 1426–1427; accounts differ on the details. The ruler of Tlatelolco was also killed. The Mexica chose as their new king Itzcoatl, Chimalpopoca’s uncle and an experienced war leader.

Itzcoatl faced a choice between submitting to Maxtla on harsh terms or fighting. According to Mexica histories, a faction of nobles led by Itzcoatl and his nephew Tlacaelel pressed for war, while some commoners feared the consequences.

The war against Azcapotzalco

Itzcoatl built a coalition. Its most important member was Nezahualcoyotl, who sought to regain his father’s throne and rallied Acolhua towns east of the lake. Forces from Huexotzinco and Tlaxcala, beyond the mountains, also joined. Some Tepanec towns that resented Maxtla, notably Tlacopan, sided with the rebels.

The war, often called the Tepanec War, was fought in 1427–1428. Allied armies attacked Azcapotzalco, which was besieged for a long period, according to the sources over many weeks or months. In 1428 the city fell. Accounts of Maxtla’s fate differ: some say he fled, while Texcocan tradition says he was killed. Azcapotzalco was sacked. Its status was reduced, and in later times it was known mainly for its slave market.

The precise sequence of battles is reconstructed from later colonial accounts, including those of Diego Duran and Fernando de Alva Ixtlilxochitl, which sometimes conflict and tend to favour the city of their authors’ ancestors.

How the alliance worked

After the victory, the three leading cities formed an enduring alliance:

• Tenochtitlan, ruled by the Mexica under Itzcoatl;
• Texcoco, restored under Nezahualcoyotl from 1431;
• Tlacopan, a Tepanec city under its ruler Totoquihuaztli, which inherited part of Azcapotzalco’s former role.

According to colonial sources, the allies agreed to wage war together and to share tribute from joint conquests: two-fifths each to Tenochtitlan and Texcoco, and one-fifth to Tlacopan. Each city also kept its own sphere of dependent towns.

The empire that grew from this alliance was hegemonic rather than territorial. Conquered cities usually kept their own rulers and customs, but had to pay regular tribute in goods such as cotton cloth, maize, cacao, feathers, gold and jade, and supply troops and labour. The Aztec state installed tribute collectors and a few garrisons, but did not govern most provinces directly.

Expansion under the alliance

The alliance quickly turned against its neighbours. In the 1430s it conquered the remaining Tepanec cities, Coyoacan, and the chinampa towns of Xochimilco to the south. Chalco, a stubborn rival in the south-east of the valley, resisted for decades before falling around 1465.

Under Moctezuma I (ruled 1440–1469), whose reign is covered in Moctezuma I and Aztec expansion, armies pushed beyond the valley to the Gulf Coast and Oaxaca. His successors Axayacatl, Tizoc and Ahuitzotl extended the empire further, and under Ahuitzotl (1486–1502) campaigns reached the Soconusco region near today’s border with Guatemala.

There were limits. The alliance suffered a heavy defeat against the Tarascan (Purepecha) state of western Mexico in 1478 and never conquered it. Tlaxcala and neighbouring states east of the volcanoes remained independent, fighting a long series of ritualised battles known as the Aztec Flower Wars.

The shifting balance of power

Although formally an alliance of equals, the partnership became increasingly unbalanced. Tenochtitlan’s population, wealth and military strength grew fastest, and by the late 15th century its ruler, the huey tlatoani or “great speaker”, was effectively the leader of the empire.

Texcoco remained an important cultural and legal centre, especially under Nezahualcoyotl and his son Nezahualpilli. Tlacopan was the junior partner throughout, and its share of tribute and influence remained modest compared with its two allies. By the reign of Moctezuma II (1502–1520), Tenochtitlan intervened openly in Texcoco’s succession, sharpening divisions that the Spanish would later exploit.

Rewriting history

The victory reshaped how the Mexica told their own past. According to the Florentine Codex compiled by Bernardino de Sahagun, Itzcoatl’s government ordered the burning of older painted books, because they contained an account of Mexica history that the new rulers found unworthy. New histories emphasised the Mexica’s divine mission and Huitzilopochtli’s guidance.

The adviser Tlacaelel, who held the high office of cihuacoatl under several rulers, is credited in some sources with promoting the cult of Huitzilopochtli and the ideology of conquest. Modern historians debate how much of this role is historical and how much reflects the pride of his descendants, whose accounts the chronicler Duran used.

Tribute and empire in practice

The best surviving picture of the alliance’s tribute system is the Codex Mendoza, a manuscript painted by Indigenous artists for the Spanish administration around 1541. Its tribute section lists provinces and the goods each owed, drawn with standard glyphs: bundles of cotton cloaks, warrior costumes and shields, bins of maize and beans, loads of cacao, bundles of quetzal feathers, gold, jade beads, copal incense and much more.

Payments were due on fixed schedules, some every 80 days, others twice a year or annually. Tribute collectors called calpixque oversaw delivery, and imperial officials could be stationed in key towns. In some frontier zones, the alliance placed garrisons or settled colonists to guard against enemies such as the Tarascans.

The system was efficient but resented. Subject towns bore heavy burdens while keeping their own rulers, which meant that local loyalty to the empire was often weak. Rebellions were met with punitive campaigns and higher tribute, a cycle that kept the empire at war almost continually.

Much tribute flowed into Tenochtitlan’s great markets and royal storehouses. It supported the nobility, rewarded warriors, paid for temple building and festivals and helped feed the city in times of famine.

Key people

• Itzcoatl (ruled c. 1427–1440): ruler of Tenochtitlan who led the war against Azcapotzalco and made the Mexica an independent power.
• Nezahualcoyotl (1402–1472): exiled prince of Texcoco who allied with the Mexica, regained his throne in 1431 and became a celebrated lawgiver and poet.
• Totoquihuaztli: ruler of Tlacopan, the Tepanec city that sided with the rebels and became the third partner.
• Maxtla: the Tepanec ruler of Azcapotzalco whose seizure of power provoked the war.
• Tlacaelel: Mexica noble and long-serving adviser, credited by some sources with shaping imperial ideology.

Myths and facts

• Myth: the Aztec Empire was a centralised state like Rome. It was a hegemonic alliance that ruled mostly through local elites and tribute, with few imperial administrators and limited direct control.
• Myth: the three allies were always equal. Formal equality gave way to Mexica dominance during the 15th century, and by 1519 the ruler of Tenochtitlan was the effective head of the alliance.

By the numbers

Timeline

• 1418: Tepanec forces kill Ixtlilxochitl of Texcoco; Nezahualcoyotl flees.
• 1426: Death of Tezozomoc; Maxtla seizes the throne of Azcapotzalco.
• c. 1426–1427: Death of Chimalpopoca; Itzcoatl becomes ruler of Tenochtitlan.
• 1428: Allied forces capture Azcapotzalco; the Triple Alliance is established.
• 1431: Nezahualcoyotl is installed as ruler of Texcoco.
• 1440–1469: Reign of Moctezuma I; expansion beyond the Valley of Mexico.
• 1478: Major defeat by the Tarascan state.
• 1519–1521: Spanish conquest; fall of Tenochtitlan ends the alliance.

Why it matters

The Triple Alliance turned three lakeside cities into the largest state in Mesoamerica in less than a century. Its tribute system, its alliances and its rivalries shaped the political landscape the Spanish found in 1519, when resentful subject peoples and independent enemies such as Tlaxcala provided the allies that made the conquest possible.