organization exists—when it links the ruler-merchant transactions with information-sharing transactions among merchants—can the multilateral reputation mechanism potentially overcome the commitment problem. Formally, when a coordinating organization exists, there is a perfect equilibrium in which traders come to the city (at the efficient level of trade) as long as an embargo has never been announced and do not come if an embargo has been announced.10 The ruler respects merchants' rights as long as an embargo has never been announced but abuses their rights otherwise. Thus, when a coordinating institution exists, trade may expand to its efficient level.
Although these strategies correspond to a perfect equilibrium, the theory in this form remains unconvincing. According to the equilibrium strategies, when a coordinating institution organizes an embargo, merchants are deterred from disregarding it because they expect the ruler to abuse violators' trading rights. But are these expectations reasonable? Why would a city not encourage rather than punish embargo breakers? Section 4.2 verifies that this encouragement is potentially credible, in the sense that beliefs that embargo breakers’ rights will be protected are self-enforcing. During an effective embargo, the volume of trade shrinks and the value of the marginal trader increases; it is then possible for bilateral reputation mechanisms to become effective. That is, there may exist mutually profitable terms between the city and the traders that the city will credibly respect. This possibility limits the potential severity of an embargo and, correspondingly, potentially hinders the ability of any coordinating organization to support efficient trade.
To support the efficient level of trade, a multilateral reputation mechanism may need to be supplemented by an organization with the ability both to coordinate embargo decisions and to enforce them, by applying sanctions on its own members. In other words, such an organization links information-sharing and coercive transactions among the merchants themselves. This organization and its expected actions are beyond the control of the ruler; his best response to them