How Fast Did Cortes Conquer the Aztec Empire?

Si Sheppard says Cortes took over the Aztec empire in what is now Mexico in two and a half years, with a couple hundred men against an empire of six million people. Pizarro did the same for the Inca empire 10 years later, in about five years.

The Aztecs and the Inca had no relationship with each other, and each side still found ways to blunt horses, armor, and Spanish weapons during its own fight. Fighters used rooftops and stones, and cut man-sized holes between buildings so horses could not chase them. While Cortes was taking a smaller city on the lake, the Aztecs broke the dikes and flooded the city, and metal armor dragged conquistadors to the bottom. Later, in the Inca war, the Inca flooded a river, burst its banks, and bogged down the cavalry. Captured swords were fixed to long wooden poles as pikes to keep horses at a distance. The Inca threw bolas, already used to hunt the great birds of South America, to tangle horses' legs. One Aztec warrior let a lance stay in his body, gripped it, and held the rider still so others could pull him from the saddle. Aztec fighters used captured Spanish prisoners to learn captured crossbows. The Inca used captured Spaniards for instruction on firearms. Manco Inca, leader of the Inca resistance, learned to ride a horse to show his people the skill was possible.

The learning curve was too steep, and the time to internalize foreign technology and tactics was too short to deploy either to real advantage.