The Aztecs were an interesting society. I wonder how much of their gratuitous sacrifices were politically calculated to keep the city states in line, and how much was due to their genuine and profound existential anxiety ("we owe the Gods for their continued sacrifice to keep the world alive -- so we better keep sacrificing to them or the sun may not come up tomorrow!")

I don't think Aztecs are a good candidate for an alternative history civ, they feel to me like a failure mode. Incas make more sense (they also had potatoes, quinoa, llamas, etc.)