Why civilizations fall

Rarely one cause.

Common pressures

Climate shifts, drought, disease, overextension, elite conflict and pressure from neighbours usually combine. Single-cause explanations tend not to survive scrutiny.

The late Bronze Age collapse hit several societies within decades.
Collapse often means reorganisation at smaller scale, not disappearance.

Continuity

Languages, religions, laws and technologies outlive the states that carried them, which is why ancient influence persists long after the political map changed.