Is designation as a “terrorist group” an effective tool for defeating rebel groups? Designation, also called proscription, could weaken rebel groups in civil conflict, as external sanctions placed on the group probably constrain its resources and capabilities. However, research on terrorist designation usually finds mixed effects. Additionally, existing research has often neglected the civil conflict environment, as well as the intrinsic distinctions between types of militant groups. Furthermore, previous studies have usually examined violence levels as outcomes, such as attack numbers, overlooking other important potential effects such as group longevity or destruction. We examine ethnically-motivated rebel groups in the civil war context, and argue that designation should contribute to group termination. We further argue that designation should lead to the specific outcome of group termination via military defeat, as opposed to other ways groups might “end.” Using a global dataset covering 1970-2016, we find support for most of our hypotheses. Designation is associated with group termination through defeat or splintering, but it is negatively related to groups giving up violence through political processes.