Closing multiple sanction loopholes

The enforcement of international sanctions is frequently undermined by multiple third-party sanction-breaking countries. This paper examines how a sanctioning country can optimally negotiate with several such loophole countries to close the enforcement gaps. We compare several sequential and simultaneous bargaining strategies. Suitably chosen sequencing, but also simultaneous negotiations under the Single-Undertaking Principle can minimize the cost to the sanctioning country by creating competitive pressure among the loophole countries. We find that, if the desire to make the sanctioning regime effective is sufficiently high, the ultimate goal of closing the sanction loopholes is achieved for all sequencing rules of ultimatum bargaining we consider. However, the equilibrium size and distribution of compensation among loophole countries differ. We characterize the optimal sequential strategy and the optimal simultaneous-offer strategy. Furthermore, for well-chosen negotiation strategies, the sum of compensations paid to multiple loophole countries is lower than if there is only one loophole country.