This paper analyses the institutional incentives and constraints of the Black Mouth Society – the traditional police of the pre-colonial Mandan and Hidatsa tribes – to understand how it successfully maintained social order without abusing power. The Black Mouth Society was a fraternal organization of middle-aged men that monitored and enforced rules created by the village council and chiefs. Two categories of institutions ensured reliable policing. First, on the front end, a long probationary period and system of unanimous consent facilitated the selection of reputable men who would wield policing power responsibly, reducing the chance of predation. However, individual Black Mouths occasionally abused their power. Therefore, on the back end, public communication created common knowledge, leading to social sanctions in the form of shame and restitution that punished abuses and limited further abuse. Thus, well-functioning self-governance, including reliable policing, is possible without a centralized state, as these tribes have demonstrated.
