Incomplete peace agreements may inadvertently increase insecurity if they trigger violent territorial contestation. We study the unintended consequences of the Colombian peace process and find that the permanent ceasefire declared by the FARC insurgency during peace negotiations with the government triggered a surge in the targeting of local community leaders. Leaders were killed by armed groups excluded from the peace process to thwart collective action and civilian mobilization, thus consolidating their dominance in formerly FARC-controlled areas. These results are exacerbated in places with judicial inefficiency and where peasants dispossessed during the conflict have started administrative process to reclaim their land.