Changing Customary Law

The unwritten nature of customary international law (CIL) enables it to remain flexible and easily adaptable to changes in States practice and opinio juris, but at the same time may be the source of substantial uncertainties when it comes to the formation, identification and development of customary norms. To investigate this issue, this paper examines the attitudes adopted by States in the aftermath of the airstrikes conducted in Syria by the USA, the UK and France in 2017 and 2018, respectively. The paper is divided into two parts: the first part includes a brief summary of the statements made by States, including the intervening States, after the 2017 and 2018 airstrikes, while the second part is devoted to the analysis of how CIL may have been influenced by the reaction of States to the airstrikes.