IMO the Tawantinsuyu are underrated; without the civil war they are almost certain to win. The worst of the smallpox had passed, they had numerical and local and supply advantages vs the Spaniards, they readily attempted, and in the case of the horse succeeded, to adopt Western technology even before the invasion became outright, having some advantages themselves (roads and cotton armor) they never saw the Spaniards as gods, had a strong centralised government and economy, and weren't surrounded by strong enemies jumping at every oppurtunitty to tear them apart.
One the other hand, the Spaniards had already gained the gold of Mexico and the abilities to conquer (Pizarro was copying his cousin, essentially), and probably other reasons I don't know of.
One the other hand, the Spaniards had already gained the gold of Mexico and the abilities to conquer (Pizarro was copying his cousin, essentially), and probably other reasons I don't know of.