Abstracts Law

The impact of the coexistence of multiple norms from different sources of international law on change to the jus ad bellum

by Katie Angela Johnston

This thesis analyses what would be required as a matter of international law to establish that a change to the jus ad bellum has occurred; that is, that states are permitted to use force in situations where it was previously unlawful under international law, or are prohibited from using force in situations where that conduct was previously lawful. More specifically, this thesis analyses how the international law norms that regulate the use of force may be modified, given that the jus ad bellum comprises multiple international law norms, from different sources of international law, some with distinctive characteristics such as jus cogens status, some of which address the same subject matter, and some of which refer to, limit the scope of, or provide exceptions to each other. It is argued that this coexistence of different kinds of international law norms impacts how those norms are modified, and so will affect how the jus ad bellum can change. The thesis analyses each of the different kinds of norm in the jus ad bellum in turn, to determine how norms of customary international law, treaty law, and norms with jus cogens status may be modified. The thesis then analyses the structure of the jus ad bellum and the relationships between the different international law norms and considers how these processes of modification are impacted by the coexistence of different kinds of norms in the jus ad bellum. In this way, the thesis seeks to identify what would be required, in terms of the practice, opinio juris and/or agreement of states, to demonstrate that a new exception to or limitation on the scope of the prohibition on force has come into existence, or that the content or scope of self-defence and collective security have changed.