Hernando Cortes was able to perform the conquest of the Aztecs mainly because of the support (tactical and military) from some of tribes that were under the rule of the Aztecs. Because multiple tribes were not happy by being under the rule of the Aztecs and even less pleased by how were they treated by them, they saw a chance to liberate themselves when the Spanish arrived, so they helped them in the conquest. Unfortunately for the local tribes, it turned out that they did not gained liberation, but instead were just under the rule of another force once the Aztec Empire fell and the Spanish one took over.