Formation of the Triple Alliance

In 1428, the city-states of Tenochtitlan, Texcoco, and Tlacopan formed the Triple Alliance, creating the political and military coalition that became the foundation of the Aztec Empire. This alliance emerged after the defeat of the Tepanec state of Azcapotzalco, which had previously dominated much of the Valley of Mexico. Historians widely regard the formation of the Triple Alliance as the beginning of the imperial system that allowed the Mexica to expand their influence across large parts of Mesoamerica during the 15th and early 16th centuries. Before the alliance was established, the Valley of Mexico consisted of numerous competing altepetl, or city-states, connected through warfare, tribute relationships, trade, and shifting political alliances. During the late 14th and early 15th centuries, the most powerful regional force was the Tepanec kingdom centered at Azcapotzalco under the ruler Tezozomoc. Tenochtitlan, although growing rapidly after its founding in 1325, remained subordinate to Tepanec authority and paid tribute while serving as a military ally. The political balance changed after Tezozomoc died around 1426. His successor, Maxtla, attempted to consolidate power aggressively and moved against rival factions within the Valley of Mexico. Relations between Maxtla and the Mexica rulers of Tenochtitlan deteriorated quickly. According to Nahua historical traditions, tensions escalated after the death of the Mexica ruler Chimalpopoca during the political crisis. In response, the new Mexica ruler Itzcoatl sought allies to challenge Tepanec dominance. One of the most important allies was Nezahualcoyotl, the exiled ruler of Texcoco, who aimed to reclaim his city from Tepanec control. Tlacopan, itself a Tepanec city dissatisfied with Maxtla’s leadership, later joined the coalition. Together, the three powers launched military campaigns against Azcapotzalco and ultimately defeated the Tepanecs in 1428. The destruction of Azcapotzalco ended the region’s previous political order and opened the way for the creation of a new imperial structure. Following their victory, Tenochtitlan, Texcoco, and Tlacopan formalized their cooperation through the Triple Alliance. Under the agreement, tribute collected from conquered territories was divided among the three partners, although Tenochtitlan gradually became the dominant member of the alliance. The coalition combined military strength, political organization, and economic resources to expand rapidly throughout central and southern Mexico. The alliance system allowed the Mexica to establish extensive tribute networks rather than direct territorial occupation. Conquered regions were generally permitted to retain local rulers as long as they provided tribute payments and military support. Goods flowing into the alliance included maize, cotton, cacao, obsidian, feathers, jade, ceramics, weapons, and luxury items. Tribute became essential to the wealth and growth of Tenochtitlan, supporting monumental construction projects, religious ceremonies, marketplaces, and military expansion. The Triple Alliance also reshaped the political and ceremonial role of Tenochtitlan. Over the following decades, rulers such as Moctezuma I, Axayacatl, Ahuitzotl, and Moctezuma II expanded the empire to its greatest extent. Tenochtitlan evolved into one of the largest cities in the world, with complex infrastructure, major temples, and a population estimated in the hundreds of thousands before the Spanish conquest. Although modern historians often refer to this state as the “Aztec Empire,” the empire itself functioned through the cooperative but unequal structure of the Triple Alliance. Texcoco remained an important intellectual and cultural center, while Tlacopan retained a smaller share of tribute and influence within the coalition. Historical Significance The formation of the Triple Alliance in 1428 transformed the Mexica from a regional city-state into the leading power of a rapidly expanding imperial system. The alliance established the political and economic framework that enabled the Aztec Empire to dominate much of Mesoamerica until the arrival of the Spanish in the early 16th century.