The Aztecs were the most developed American civilization until the arrival of the Spaniards, who decimated them.
The Spaniards came from a developed continent, with superior warfare technologies. The Spaniards held cannons, horses, swords, while the Aztecs still did not even know gunpowder and white guns.
In addition, the Spaniards carried diseases for which the Aztecs had no contact, and therefore, immunity.
The amount of years for service varied and was decided by the contractor, for adults it was typically around 4 to 7 years but it wasn't always only seven years.
