A Game Theory Analysis of the Threshold Requirement

Abstract

In recent years the interpretation of the ad bellum rules has been readjusted so as to permit forcible responses against terrorism under more lenient conditions. Yet the threshold level of provocation that legitimizes a full-scale war in response remains relatively high. This observation is especially puzzling insofar as customary international law reflects the practice of (strong) states, because these states, as we show, can benefit from credibly lowering their tolerance towards terror attacks. We argue, however, that a low threshold requirement cannot be sustained; it is a futile measure to fight terrorism since normally it is not renegotiation proof (albeit credible). Namely, were a strong state to wage a full-scale war following some mild provocation by a weak one, both parties are better off renegotiating their way back to the status quo ante. On the other hand, renegotiation may fail if transaction costs are high enough. In which case, intolerant threshold strategy by the strong side does become renegotiation proof. Consequently, a strong state is expected to violate the ad bellum threshold rule in these circumstances, and decrease, thereby, the terror level from which it suffers.

Keywords: rules of war, threshold requirement, jus ad bellum, game theory, proportionality, critical mass