Primogeniture

A disputed succession gives each faction an incentive to rally around its preferred claimant. Primogeniture removes much of that ambiguity in advance: birth order selects one person through a rule that is easy to observe and difficult to reinterpret after the throne becomes vacant.

That common expectation is the mechanism. Once people expect others to recognize the eldest son, supporting him becomes safer and rival claims become harder to coordinate. The rule therefore works as a focal point: not by proving who deserves power, but by making one outcome conspicuous enough that competing coalitions struggle to form.

An obvious successor can still be incapable, unacceptable, or opposed by actors powerful enough to ignore the rule. Primogeniture solves ambiguity only when the relevant parties recognize the convention; it cannot guarantee fitness, fairness, or obedience. Its coordination benefit must therefore be kept separate from any claim that its chosen outcome is good.