The Mayan collapse is no great mystery. Constant warfare between the city-states eventually took its toll. The treasure needed to maintain a vital civilization was pee’d into the winds of war. Even a short drought or period of intensified hurricanes (they’re periodic and devastating on that flat land that’s barely above sea-level) was probably enough to push the “tilt” button.
Civil Wars wrecked the Roman Empire. That and Bread and circuses. Small wars can bled a civilization.