Understanding the tangled web of cause and effect that potentially links poverty and violence is a task that has long stymied social scientists. Does war cause poverty, or vice-versa? Or perhaps other factors – such as societal hatreds or divisions – cause both economic stagnation and war. Maybe all three of these are operating at once. This is no matter for ivory-towered thumb twiddling – foreign aid priorities hinge critically on the answer.

In an earlier Vox commentary, World Bank economist Simeon Djankov and Marta Reynal-Querol of Pompeu Fabra claim that the evidence weighs against poverty-induced violence. Yet their arguments fail to account…