Excerpt:
The researchers also examined a common factor in the collapse of societies with good governance: leaders who abandoned the society’s founding principles and ignored their roles as moral guides for their people.
What does that remind you of?
societies collapse after the marginal return on investment in societal complexity goes negative. not necessarily immediately after, there's usually some desatbilizing incident that catalyzes the process once that point has been reached.
I recommend The Collapse of Complex Societies by Joseph Tainter