In this paper, I empirically investigate how openness of political institutions to diverse representation can impact con ict-related violence. By exploiting plausibly exogenous variations in the number of councillors in Colombian municipalities, I develop two sets of results. First, regression discontinuity estimates show that larger municipal councils have a considerably greater number of political parties with at least one elected representative. I interpret this result as evidence that larger municipal councils are more open to political participation by more groups in society. The estimates also reveal that smaller parties are the main bene ciaries of this greater political openness. Second, regression discontinuity estimates show that political openness substantially decreases con ict-related violence, namely the killing of civilian non-combatants. By exploiting plausibly exogenous variations in local election results, I show that the lower level of political violence stems from greater participation by parties with close links to armed groups. Using data about the types of violence employed by these groups, the provision of local public goods, scal outcomes and coca cultivation, Iargue that armed violence has decreased not because of power-sharing arrangements between the armed groups linked to the parties with more political representation, but rather because armed groups with less political power and visibility are deterred from initiating certain types of violence.
