Trauma can lead to vengeance (Image: David Brauchli/AFP/Getty Images)

THE past two decades have seen an increase in mass violence around the world, including wars, armed conflicts, human rights abuses and terrorism. Effectively dealing with these problems requires an understanding of the motivations that drive people to violence – sometimes to the point of self-sacrifice, as in the case of suicide bombers.

Unfortunately, attempts to develop such an understanding rarely go beyond value judgements, ideological beliefs and vacuous labels such as “fanatic” or “religious extremist”. What we need instead is a scientific analysis.

Acts of violence do not occur in a …