© The Author(s) 2017. Recent research emphasizes the effectiveness of biased third parties and their use of leverage in resolving conflicts. However, scholars fail to explore systematically the conditions under which conflict management strategies straddle the confines between mediatory techniques and approaches more commonly associated with joining behavior. This article examines the threshold between neutral conflict management and overt joining by offering a model of third-party intervention based on the notion of international social proximity and situated within the familiar opportunity–willingness framework. Our arguments are tested with a novel combination of data on biased joining from Corbetta and Dixon and data on neutral mediatory efforts from Frazier and Dixon. Our findings reveal that the application of biased leverage and mediation is rare but salient, and asymmetrical ties between third parties and combatants explain their occurrence.