Common ecology quantifies human insurgency

Many collective human activities, including violence, have been shown to exhibit universal patterns(1-19). The size distributions of casualties both in whole wars from 1816 to 1980 and terrorist attacks have separately been shown to follow approximate power-law distributions(6,7,9,10). However, the possibility of universal patterns ranging across wars in the size distribution or timing of within-conflict events has barely been explored. Here we show that the sizes and timing of violent events within different insurgent conflicts exhibit remarkable similarities. We propose a unified model of human insurgency that reproduces these commonalities, and explains conflict-specific variations quantitatively in terms of underlying rules of engagement. Our model treats each insurgent population as an ecology of dynamically evolving, self-organized groups following common decision-making processes. Our model is consistent with several recent hypotheses about modern insurgency(18-20), is robust to many generalizations(21), and establishes a quantitative connection between human insurgency, global terrorism(10) and ecology(13-17,22,23). Its similarity to financial market models(24-26) provides a surprising link between violent and non-violent forms of human behaviour.