Decentralization is increasing in all parts of the world. Assessing the efficiency of decentralization as a means to mitigate ethnic conflict is then of primarily importance. This paper builds a simple model of decentralization as an empowerment mechanism. It suggests that decentralization could promote peace conditional on a set of countries and groups characteristics. Typically, decentralization should empower minorities which are small at the national level, while representing a critical mass of the population in the regions they live in. Empirical results confirm that decentralization impacts ethnic conflict only when those conditioning factors are controlled for. Furthermore, decentralization dampens all forms of ethnic violence for groups spatially concentrated enough and/or for groups having a local majority. In contrast, it fuels protest and even rebellion for groups lacking one. The paper then highlights the crucial need to build checks and balances mechanisms at the regional level for local minorities not being harmed by the decentralization process.