I read the English version of Cortez’ account.
As they approached the city, they saw what they thought was a red mountain.
I was a pyramid...The red was blood from the sacrifices.
The Aztec’s own history records how many 10s of thousands on certain days the killed for their god.
Cortez was able to defeat the Aztecs only with the help of the other ethnic groups in central Mexico who hated the Aztecs. They may not have been very happy with Spanish rule but at least the Spanish weren’t taking their people for human sacrifices.