While this may be true:

Time and again history has shown us that when inequality becomes unsustainable, even the most powerful republics fall.

at what point does inequality reach the tipping point. How long can unrest be suppress with bread and circuses?

How long can brutal suppression prevent revolts. Use North Korea as an example. Can be no more extreme inequality than the contrast between the North Korean Leadership and the general population.

History might tell us something but it is vague.

TEK