"New findings ... highlight the complexity of geopolitics in Aztec era Mesoamerica and illustrate how the relationships among ancient states extended beyond warfare and diplomacy to issues concerning trade and the flow of goods." Source: Science Daily.
Note: "The researchers focused on an independent republic called Tlaxcallan [Tlaxcala] in what is now central Mexico, about 75 miles east of modern Mexico City. Tlaxcallan was founded in the mid-13th century and, by 1500, was effectively surrounded by the Aztec Empire -- but never lost its independence. In fact, Tlaxcallan supported Cortés and played a critical role in the Spanish Conquest of Mexico in the 16th century."
Comment: The Aztec empire only lasted for around 200 years. (Its capital city Technochtitlan was founded in 1325 and the empire was defeated by the Spanish and their local allies in 1521). Following a pattern common in the ancient, medieval and modern worlds, the Aztecs didn't seem to understand (or didn't care) that they were destabilizing themselves by creating so many enemies with their harsh rule.