On Oligopoly And Social Norms.

At least after they reach a certain point, distributional coalitions have an incentive to be exclusive … whatever quantity an entrant would sell must either drive down the price received by those already in … [or] there will be more to distribute to each member of the coalition if it is a minimum winning coalition

With implications for aristocratic intermarriage:

if the sons and daughters of the ruling group are induced to marry one another, the growth of the ruling group can be constrained in ways that preserve a legacy for all the families in it