The task of this chapter is to describe the input of IL into decision-making about targeting in the three cases under investigation. In order to know what we are looking for we need a definition of what IL is. The theory of IL proposed in Chapter 2 derives the definition of IL from the way in which compliance with law can change behaviour. For the task at hand this is not a suitable approach to identifying IL because it hinges legality on what this part of the book wants to evidence and understand: the net effect of recourse to law on behaviour. For the purpose of grasping only the extent to which the US recurs to IL, I therefore rely on a thinner conception of IL, one that uses the form of norms to identify them as laws.

Section 1.3 discussed two alternative ways in which scholars of IR have attempted to define IL by its form: the liberal institutionalist concept of ‘legalisation’ and a positivist approach that takes municipal law and its characteristics as a blueprint for the identification of IL. I choose ‘legalisation’ as a point of departure here, first and foremost because the parameters of this approach are based on observed developments in international relations rather than on domestic law. Second, unlike a positivist definition of law, ‘legalisation’ conceives of the subjection of decision-making to law as a matter of degree. The three proposed parameters – the precision of legal norms, the delegation of their interpretation and the obligation pull they exert – provide ‘identifiable dimensions of variation’. They allow me to measure the extent to which actors follow their interests and normative beliefs in war via recourse to law.