Mediation, peacekeeping, and sanctions – the international community has tried various intervention methods to reduce conflicts around the world. This paper examines the humanitarian consequences of international efforts with a focus on the fluctuation of militant violence against civilians. We argue that external interventions in internal conflicts alter political, military, and economic balance among militant groups, creating both intended and unintended consequences depending on the militant characteristics such as adaptability, co-optation and rivalry. By altering political balance among militant groups, non-inclusive mediation increases the violence of excluded militant group, while decreasing the violence of included militant group. By altering military balance among militant groups and creating a security vacuum in one area, forceful peacekeeping might reduce the violence of the targeted group, but at the same time, might increase the violence of the rival group that has been co-opted with host government forces. By altering economic balance and hurting one group more than others economically, sanctions might decrease the violence of the non-adaptable militant group that fail to adjust, but inadvertently increase the violence of adaptable groups that can easily shift their resource bases to other lucrative sources. We test these arguments using the interrupted time-series intervention analysis in the context of the conflict in the Democratic Republic of Congo, one of the longest running civil wars featuring multiple militant groups. Our findings about the differential impacts of intervention measures on diverse set of militant groups have implications for external intervention in internal conflicts.