Chicago Journal of International Law

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The principle of proportionality is a central feature of international law regulating modern military engagements. Yet the legal status of proportionality in international law is far from clear. Two major international treaties—the Rome Statute and the 1978 Additional Protocol to the Geneva Convention—address war crimes and provide distinct definitions of the crime of disproportionate use of force. Many of the world’s major military powers are not signatories to either treaty. Consequently, the only framework of legal accountability for alleged proportionality violations committed by those nations is customary international law. Furthermore, in non-international conflicts no treaty law respecting proportionality exists, meaning that customary international law again is the only binding law available. Given the importance of the definition of proportionality to policing modern military conflicts, reducing ambiguity regarding the legal elements of proportionality would be a salutary development. This Comment, drawing on doctrinal and realist policy analyses, argues that the legal elements of proportionality in customary international law can be clarified through the adoption of the definition of proportionality provided by the Rome Statute as customary international law.