Introduction: promoting restraint in war

Over the last decade, changes in the nature of conflict have generated profound operational challenges for international humanitarian organizations. The number of non-international armed conflicts doubled between 2001 and 2016, rising from fewer than 30 to more than 70. The number of armed groups fighting in them has also multiplied: more armed groups emerged in the last decade than in the previous century. Humanitarian organizations struggle to assist victims of these armed conflicts and to persuade fighters to act with restraint toward those individuals who are not, or no longer, taking part in hostilities. New research was required to identify sources of influence on battlefield restraint to inform operational activities. We present a theoretical framework that identifies the sources of norms of restraint in state and non-state armed groups. We argue that humanitarian organizations ought to broaden their notions of the processes that influence the socialization and uptake of norms of restraint and mobilize new societal actors to the cause of limiting violence. In our framing of the empirical articles in the collection, we argue that the structure of armed organizations and their embeddedness in local communities heavily influence how group norms and internal rules are formed and reinforced. While hierarchical militaries can largely be influenced by top-down discipline, restraint among more decentralized armed groups is strongly influenced by societal actors external to the group.