Conflicts over resources with poorly defined property rights have fuelled both deforestation and violence in the Brazilian Amazon. However, what happens when the State enhances its ability to monitor and enforce existing environmental laws? We study the case of the list of Municípios Prioritários, a policy that allocates additional resources to verify compliance with environmental laws in municipalities with high deforestation rates. Employing a difference-in-differences approach, our findings suggest that an improvement in the ability of the State to monitor and enforce environmental laws can reduce conflicts over the appropriation of value from resources with poorly defined property rights. Consistent with existing studies, we also find that the policy led to a reduction in deforestation rates in the Brazilian Amazon. Finally, we discuss the limitations of the current approach to curb violence in a region where the activity of mafias has considerably grown since the turn of the twenty-first century.