"Hate was just a legend.
And war was never known.
The people worked together.
And they lifted many stones."
The Aztecs were in a near constant state of war with their neighbours at a cost of tens, if not hundreds, of thousands of casualties per year. The wars were fought for territorial possession, to capture victims to sacrifice to their literally blood-thirsty gods, and sometimes just for the hell of it.
It's worth noting that the Aztecs were not an ideal civilization by any means and Hernando Cortez could not have conquered it if it weren't for the surrounding civilizations who, tired of being domineered by a group of warlike savages, decided to settle for the lesser of two evils and help the Spanish (who admittedly were not much better).
The poem is accurate on the fact of Cortez being a killer however.