New insights into the psychology of individuals and large groups in a world of changing conflicts

The character of armed conflict has changed dramatically. The use of overwhelming force no longer brings victory and success. Under what conditions do supposedly weaker conflict actors ‘outpower’ stronger actors? This article argues that, throughout human history, those most willing to engage in and sustain extreme conflict have not been rational actors but ‘devoted actors’ driven by faith in defending or advancing their non-negotiable ‘sacred values’, whether religious or secular. Bringing into dialogue insights from large group psychology, neuroscience, and epigenetics with political science, this article demonstrates how two factors can help explain apparently non-rational elements of human functioning during armed conflict: first, the biological substrate helps elucidate why and how rational actor models seem to underestimate the influence of ‘right and wrong’ in people’s behaviour; second, the complex psychology of large groups often drives people to engage in action that may not be in their own individual interests.