Does the UN Charter’s use of force regime remain relevant and effective in regulating or constraining the behavior of states? This chapter answers this question in part by examining the incidence of the transnational use of force since 1945. The chapter finds that the level of transnational use of force has not significantly increased, despite the emergence of new security threats. The chapter also investigates how states engage with the Charter’s use of force regime by examining their justifications for military action. The chapter finds that states remain committed to the existing UN Charter’s legal framework. The proportion of transnational instances of the use of force for which states provide formal justifications to the Security Council has remained relatively static since 1945. The changing patterns of justificatory discourse also reveal limited reliance by states on legally contested bases for using force, suggesting an absence of state claims for the adaptation of black letter law. The one notable exception reflects evolving recognition that the right of states to exercise self-defense against nonstate actors located in other states prevails over the territorial integrity of the state where force is used. The chapter also finds increasing reliance by states on extralegal justifications, which frequently complement contested legal arguments. The use of extralegal justifications in this way suggests that even when states use force in circumstances that are difficult to reconcile with the black letter law of the Charter, they do not directly challenge the applicability of the Charter’s use of force regime.

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