Chicago Journal of International Law

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In recent years, ad bellum rules have been interpreted more leniently so as to permit forcible responses to terrorism. Yet the threshold level for an “armed attack” that legitimizes full-scale war in response has remained relatively high. This observation is especially puzzling insofar as customary international law reflects the practice of (strong) states, which, as we show, can benefit from credibly committing to lowering their tolerance towards terror attacks. Why is the threshold requirement relatively tolerant? What would be the critical mass of terror beyond which a full-scale war is legitimate? Under what circumstances are states expected to violate the ad bellum threshold requirement?

This Article seeks compelling answers to these questions using game theory. We argue that a low ad bellum threshold requirement (an “intolerant strategy”) is a futile measure to fight terrorism, since normally it cannot underlie a renegotiation-proof equilibrium. Namely, were a strong state to seriously consider waging a full-scale war in response to repeated, low-level terror attacks sponsored by a weak state, both parties would be better off renegotiating their way back to the status quo ante. On the other hand, renegotiation may fail if transaction costs are high enough, which ultimately makes the intolerant strategy sustainable and the equilibrium level of terror lower. The overall conclusion is thus counterintuitive: an effective intolerant strategy in the War on Terror is beneficial for victim states, but implausible unless the barriers towards a nonviolent arrangement are sufficiently high.

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