The Spaniards “discovered”, “conquered” and murdered them.
I do not think you need the quotes on discovered or conquered. They clearly did both. As for “murdered”, I am sure quite a bit of that happened. But for context, I suggest you read “The Discovery and Conquest of Mexico” by Bernal Diaz. It is the only first person account we have of the Conquest. There are, I recall, 5 letters to the Emperor of Spain from Cortez, but they are kind of special pleading, so to speak.
There is one other contemporary partial account, with much less detail, it mostly agrees with Diaz’ book.
The Aztecs and the neighbors were awash with human sacrifice and cannibalism. Their replacement by the Spanish was definitely a step up.
The real problem were the diseases brought over by the Spanish and other Europeans. Those diseases killed off many millions.
But you cannot blame the Europeans for that, any more than you can blame the Black Death on the Arabs.
The French & British found the same practices in North America; cannibalism (eating one’s captured enemies) was very common, but we’re supposed to believe in the “noble savage”. Revisionist BS...