In the years since the 1999 NATO airstrikes on Serbia to prevent ethnic cleansing of the Kosovar Albanians, international law has been moving in fits and starts toward recognition of a limited right of humanitarian intervention in the absence of Security Council approval. But all the ingredients necessary for the crystallization of customary international law were not present until the April 14, 2018 U.S./French/U.K. airstrikes on Syrian chemical weapons facilities. This article examines the unique features of the April 2018 airstrikes – the context of a crisis of historic proportions, the focus on preventing the use of chemical weapons, the collectivity of the action taken, the limited targets and collateral damage, the explicit invocation of humanitarian intervention by the UK as the legal justification, and the subsequent statements of international support and opposition – and analyzes how the Syrian airstrikes have changed international law concerning humanitarian intervention.


humanitarian intervention, responsibility to protect, chemical weapons, Syria, airstrikes, customary international law, U.N. Security Council, use of force.

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19 Chicago Journal of International Law (2019 forthcoming)


COinS Michael P. Scharf Faculty Bio