A Complex Legal Battlefield: Ensuring Respect for the Rules of Armed Conflict in Support Relationships Between States and Non-State Armed Groups

Contemporary armed conflicts frequently involve one or more non-State armed groups, such as rebel groups or militias. While these groups operate independently, they often receive material resources, financial assets, and/or operational support from States. For their part, States have long recognized that supporting armed groups allows them to influence conflicts without intervening directly with their own troops. However, such support frequently facilitates or contributes to violations of the rules of armed conflict by non-State armed groups, including war crimes, genocide, or crimes against humanity. This is not merely incidental: Circumventing their legal obligations and avoiding responsibility for violations forms one of the key motivations for States to establish such support relationships.
This study examines the international obligations of States to ensure respect for the rules of armed conflict when supporting non-State armed groups. It shows that existing rules of international law found across various Treaties and Conventions– though not specifically designed to regulate support relationships – do contain relevant obligations ranging from prohibitions on contributing to violations of the law of armed conflict to obligations to prevent, suppress, and respond to such violations. The study argues that these existing obligations provide a comprehensive framework for regulating support relationships and for holding States accountable when their assistance enables violations of the rules of armed conflict. In doing so, it contributes to a better understanding of how international law applies to support relationships and similar forms of proxy warfare, and highlights the legal responsibility of States in these constellations.