explaining that this sort of violence common in civil wars, namely that violence that is significant by its number of victims, its ‘barbarism’ (or brutality) and the fact that both victims and executioners have had a peaceful performance in their past interaction (i.e. neighbours). The research tries to be confined to that kind of violence in civil wars, and the work principally provides an explanation to the spatial variance of that dependent variable. Temporal approaches are suggested, but not deeply developed in comparative terms. As civil wars are frequently battled by means of some sort of irregular warfare by one or both contenders, Kalyvas embodies his explanation in the constraints of irregular wars, specifically the ability of competitors to hide themselves behind civilian population, and the uncertainty around who is an enemy and who is neutral in such an environment. Enemies can be hidden among the apparently supporters of a community, and contenders can only deal with such informational problems in an efficient ways by exercising violence against previously selected defectors. The efficient way of doing so is waiting for spontaneous civilian informers, an action more critical in highly competed areas, where powers are balanced and, consequently, sovereignty is fragmented. On the other hand, the probability of denunciations grows with the level of control that one side has in a given area. The more the control one side has, the risk of retaliation by the other side that informers have to face is less, but the probability of real defection and shifting to the other side is lessened also, compromising the credibility of those numerous and spontaneous informers. Political actors do not search for violence as the first-best option to prevent both shifts and defections, because they generally prefer selective, limited violence (that reduces the probability of shifts and defections by deterrence) to arbitrary, massive violence (that increases the likelihood of those outcomes). The mechanism follows a tree iterating game where political actors decide if they want to use violence, depending on the degree of control over that territory, but they confront an “identification problem”. Then, individuals decide if the benefits of denunciation (old feuds and grievances) are higher than the risks of doing so, given the level of control of the own side in the territory. A group of institutions to make denunciation easier and more anonymous are required to increase the likelihood of that event, but they perform