Abstract Ethnic groups employ different strategies to pursue demands for self-determination. While some act within conventional channels of political contestation, others choose non-conventional strategies, including violence and rebellion. We conceive of this as a result of bargaining between group and state and argue that both sides’ institutions affect the likelihood of escalation. Specifically, groups with traditional authorities have the capacity and incentives to escalate conflicts. Only when such institutions are matched with internal accountability mechanisms can groups credibly commit so that bargaining failure and violence less likely. Similarly, states with open elections can tie their hands more effectively, and constitutional regulations of traditional authorities formalize state-group interactions, which also mitigates the effect of traditional authorities on conflict. We use new global data on groups that demand self-determination, their traditional political institutions, and their strategy choice from 2005 to 2015. We find support for our argument using various identification and estimation approaches. Groups with traditional authorities are much more likely to use violence, a finding that is not sensitive to the omission of unobserved confounders. Furthermore, this relationship is moderated by group-level audience costs and the strategic environment provided by the state. Our findings advance new perspectives on the interactions of customary and national institutions in determining subnational conflict.