Violent communal conflicts between identity-based groups are a severe threat to human security and development. While most communal conflicts take place in civil war-affected countries, communal conflict is not an inevitable byproduct of civil war. What explains communal peace in civil war? Existing research tends to overlook interlinkages between communal conflict and civil war, meaning that knowledge on how armed groups exacerbate or mitigate communal conflicts is limited. Combining insights from research on communal conflict and non-state armed groups, this study proposes that communal conflicts are less severe in areas controlled by legitimacy-seeking armed groups that seek acceptance for its political authority and right to rule from domestic and international audiences. Legitimacy-seeking armed groups have greater incentives to develop institutions and practices that prevent both communal conflict onset and escalation, which helps keep communal peace. The study examines the argument through a natural experiment in western Côte d’Ivoire, where more legitimacy-seeking and more legitimacy-indifferent armed groups came to control proximate and highly comparable communities because of an arbitrary ceasefire line. Using process-tracing to analyze unique interview and archival sources, the study demonstrates that communal conflicts were far deadlier in areas controlled by the more legitimacy-indifferent militias than in areas controlled by the more legitimacy-seeking Forces Nouvelles rebel group. These findings highlight that armed groups can be both agents of wartime disorder and order, and contribute new insights on communal peace in the shadow of civil war.