The Spanish invaded the Aztec when they were not expecting it. They Aztec thought the Spanish were gods because of a prophecy. The Spanish were actually just looking for gold and goods and other delicacies. They went and attacked the Aztec with a bunch of weapons that the Aztec had never seen such as guns cannons and swords. The Spanish also had armor and horses and horses with armor on them. Even though the Aztec had way more men in their armies they still lost because they were behind in technology and they got sick with a lot of the Spaniards diseases, which also weakened their armies and people. Because how are the Aztec's people supposed to fight when they are sick and dieing and do not know how to fight back against the Spaniards weapons.
The Encomienda System was a system in Spanish America that gave settlers a right to tax the local Indians and summon them for labor; they also were not given juridical authority.
It was good for the Spanish but not for the Incas because the Incas were forced to work against their will and if they refused them would either be imprisoned and forced to work or killed and if they ran away they would usually be killed. It mostly benefited the Spaniards. If I was a Spaniard back then I probably would have supported it because then I would not have to do my own work. But If I was Inca I definitely would not support it because I would not like to be a slave and have to work for these Spaniards that I thought were coming to help us and make us a better civilization but were really just trying to destroy us and steal our stuff.