The Classic Maya Collapse
Over the 800s and 900s, the great cities of the Classic Maya — among the most sophisticated of the ancient Americas, with full writing, astronomy, and mathematics including the concept of zero — were abandoned one by one. The likeliest culprit is a run of severe multi-decade droughts that their dense populations and warring, rigid elites could not withstand. It is climate stress amplifying every existing strain at once — the Akkadian and Bronze Age story, retold in a New World key.
An environmental shift (drought, cooling) strains food and water systems, amplifying every other tension at once.