The answer is a) Add a bill of rights to the constitution
To my knowledge most of the Aztecs died off from the diseases brought over from Europe.
One advantage was most likely due to Cortes having artillery? The Aztecs had superior weapons, but The Spanish had armor.
Maybe someone else knows more on the topic, but this might be a good starting point.
-- the climate in various regions; -- the laws of Physics; -- the flora or fauna; -- the status of medical research; -- the general impression of Congress' effectiveness; -- the moon's phases.