Conversation so far:
When did the Spanish colonization of Mexico begin?
The Spanish conquest of Mexico is generally understood to be the Spanish conquest of the Aztec Empire of 1519–21.
What happened during the Spanish colonization of Mexico?
The Spanish conquest of the Aztec empire.

Question: What was so spectacular about the conquest of the Aztecs?
Self-contained rewrite: What was so spectacular about the Spanish conquest of the Aztecs in 1519?