Question

what aspects of Aztec society made them vulnerable to attack with the arrival of the Spanish in the sixteenth century

Answer 1

Aztecs believed that the conquistadors were gods, so they've let them in their cities, which let to their demise

Answer 2

- Their willingness to appease the Gods.
Aztec did a lot of human sacrifice and when the Spanish arrived in 1508, the Aztecs though they were supernatural beings and were willing to do anything for them.

- Their will for independence.
While some other provinces were captured (about 38), some places decided to stay independent. Due to this, they had no allies as the Spanish and other provinces acquired. Basically the Aztec were not a united empire.

- Their isolation
The Spanish were exposed and immune to things like smallpox and influenza. Because the Aztec were never exposed, upon exposure tens of thousand were wiped out by an outbreak.