This study, conducted in five fragile African states (DRC, Nigeria, Mali, Cameroon, CAR), shows that in several fragile African states, the weakening of state authority stems from precarious governance, corruption, extractive institutions, and resource-related conflicts. Faced with the state’s inability to ensure security and justice, parallel customary, religious, militia, or popular systems develop, sometimes gaining more legitimacy than official institutions. These alternatives address immediate needs but generate violence, territorial fragmentation, and the erosion of the rule of law. Popular justice arises from distrust of the state, judicial inefficiency, and the influence of community norms. Mixed-methods, multi-site approach combines local qualitative analysis with quantitative generalization, reinforced by triangulation and tools such as NVivo. The results show that popular justice emerges as a response to state dysfunction characterized by insecurity, corruption, judicial absence or delays, poverty, and territorial fragmentation, with specific forms depending on local contexts (witchcraft in the DRC, security struggles in Nigeria, the role of the Dozos in Mali and the CAR). The multi-site model reveals common factors (state weakness, breakdown of trust, parallel governance) and contextual variations, shedding light on the development of alternative justice system. The study proposes a polycentric governance model integrating the state, local actors, and traditional mechanisms to restore state authority and reduce vigilante justice. The proposed solutions are based on inclusive governance, combating corruption, institutional strengthening, and integrating traditional mechanisms within a reformed legal framework.