As sherif noted, despite the fact that the competitive behavior of the boys in the warring camps seemed "wicked, disturbed, and vicious," what actually triggered their evil behavior was

One factor could be that terrible or evil situation has happened to them during the camps. Or it can be the cause of peers that have bad influence of the boys which made them do what they had did. The triggered actions can be a cause of mindless thoughts in situations that they cannot understand.