Identifying co-parties to armed conflict in international law

Think tank: Chatham House

Author(s): Alexander Wentker; Miles Jackson; Lawrence Hill-Cawthorne

March 6, 2024

This report from UK think tank Chatham House examines how states, international organisations and armed groups become parties to war.

States have often relied on each other’s support to wage wars. But, as military technology advances, contemporary armed conflicts are increasingly characterized by complex patterns of cooperation involving states, international organizations and non-state armed groups. These patterns make it difficult to identify who among the cooperating partners qualifies as a party to conflict – referred to in this research paper as co-parties. But that status has significant legal consequences in the regulation of armed conflict.

The need for clarity around co-party status has therefore never been greater. This research paper aims to provide a roadmap to establish who is party to an armed conflict and the legal implications of that finding.

The paper draws on illustrative examples from both recent and current conflicts to analyse what co-party status means and how parties to armed conflicts are identified as a matter of international law.