That correlation might be reversed, though. The author of The Great Leveler makes the argument that in peaceful times, inequality almost always rises to the maximum level that society can bear. It remains that way until a destabilizing event occurs (plagues, state collapse, destructive revolution, mass-mobilization warfare) which decreases inequality (mostly through wealth destruction - the wealthy have the most to lose).

So it's possible that rather than high inequality leading to destabilization, it's the opposite: destabilization leads to decreased inequality.