Inane cliches/truisms you could go the rest of your life without hearing again

[Franknburger]

Empires breaking apart due to internal conflicts / turbulences.

Stops just when it starts to get interesting: Economic crisis? Caused by natural disasters (e.g. earthquakes), climate change (flooding, droughts), changes in regional trade flows?
Distribution imbalance (a small group amassing too much power / wealth)? Over-ambitious reforms, which were not accepted by the population or (parts of) the traditional elite? Dozens of possible causes, that somebody has been too lazy to look into ...