According to the literature of conflict prevention who deals with the effectiveness of preventive action, chances of success tend to rise when prevention is structural, and when it occurs within a multitrack framework. The results of this research indicate that, before dealing with the effectiveness of preventive action, one must verify the conditionalities of preventive action, which limit or encourage the involvement of international actors in the prevention of violent conflicts. It is argued that international preventive action is conditioned by three elements: (i) the construction of a concept of conflict prevention; (ii) the creation of mechanisms to implement the concept; and (iii) the interpretation of the local context as being preventable by international interference. In the cases of Kosovo and of the former Yugoslav Republic of Macedonia, the promotion of a preventive discourse by international actors is not enough to induce to institutional changes. Besides, even when mechanisms are available to potential international preventors, they would only be implemented if the situation in loco is interpreted as being preventable. The cases under analysis reinforce the main argument of the literature and demonstrate that chances of success of preventive action were lower in Kosovo because of inaction and also superficial, late and uncoordinated action of the few relevant actors. In its turn, preventive action in Macedonia had higher chances of success because it was a structural and multitrack effort of different actors, thanks to the interpretation of the situation in loco on the very edge of the crises.