The Moche
On a desert coast that gets almost no rain, the Moche built irrigation canals off the rivers, raised adobe pyramids, and produced metalwork and ceramics of extraordinary skill — portrait vessels so individual that archaeologists can recognise the same person across different pots. They had no writing. Their art shows warfare, prisoners, and ritual killing in unflinching detail, and excavated burials match the scenes closely enough that the pots appear to be documentary. They declined around 600–800 CE amid evidence of severe El Niño flooding and drought.
An environmental shift (drought, cooling) strains food and water systems, amplifying every other tension at once.