When the Spaniards arrived in Tenochtitlan, Moctezuma asked his greatest rival,
King Zuangua of the Tarascans, for aid in the case there was war.
Zuangua thought that Moctezuma would use the Tarascan troops as fodder to defeat the Spaniards then conquer his own kingdom. He rebuffed the Aztec ambassadors, saying that the Aztecs had brought ruin upon themselves because "they merely sang songs to their gods, instead of carrying wood to their temples to keep the fires burning." (Tarascan temples had ever-burning fires.)
After Moctezuma was killed and the Spaniards besieged the city of Tenochtitlan, the Aztecs again asked the Tarascans for help. Zuangua had died of smallpox, and his son Tzintzicha Tangaxoan was now king. The Aztec ambassadors didn't know this and asked to meet Zuangua.
Tzintzicha Tangaxoan said "Alright," then executed every Aztec so that they could meet Zuangua in the afterlife.
Then the Aztecs surrendered and the Tarascans were conquered.
What if Zuangua had decided to choose the devil he knew before the devil he didn't and together defeated Cortes?