War as a moral imperative (not just practical politics by other means).

We present findings from one survey and five experiments carried out in the USA, Nigeria and the Middle East showing that judgements about the use of deadly intergroup violence are strikingly insensitive to quantitative indicators of success, or to perceptions of their efficacy. By demonstrating that judgements about the use of war are bounded by rules of deontological reasoning and parochial commitment, these findings may have implications for understanding the trajectory of violent political conflicts. Further, these findings are compatible with theorizing that links the evolution of within-group altruism to intergroup violence.