Humanitarian Intervention: Fairy Tale about One Swallow Which Made Summer?

In its final report on aggression and the use of force, the International Law Association opined that the only way in which unilateral humanitarian intervention could possibly be seen as a legal exception to the prohibition of the use of force is if State practice and opinio juris were to be found establishing its status as an additional exception in customary international law. After the airstrikes conducted by the US, the UK, and France against Syria in April 2018, which took place in reaction to unprecedented usage of chemical weapons against civilian population by regime of Bashar Asad, some States and part of scholars argued that this permissive rule (exception) has already crystalized and humanitarian intervention became part of international law. The aim of this article is to assess whether these opinions are relevant or whether they are simply premature. The text is divided into three parts. Firstly, legality of humanitarian intervention is considered in the framework of the UN Charter and customary international law on the use of force based on evaluation of scholarly debates and the most prominent examples of State practice before 2018. Then, the article describes methodology that is employed in relation to the creation (modification) of customary international law in general and peremptory norm concerning the prohibition on the use of force in particular. This part analyzes how possible normative changes of jus ad bellum should be assessed. The third part evaluates justifications and reactions of States with respect to the use of force against Syria in April 2018 that were presented by the international community of States. The article concludes that the concept of humanitarian intervention remains still illegal even after the airstrikes against Syria from 2018, what conforms to the prevailing opinion presented in contemporary scholarly literature. Even though the positive echoes identified in State practice (and doctrine) are yet premature, they indicate that process of gradual normative change has already been triggered. At the same time, the expectations concerning crystallization of a new possible exception to the general prohibition on the use of force should not be too exaggerated.