Farming and Fighting: An Empirical Analysis of the Ecological-Evolutionary Theory of the Incidence of Warfare

Abstract

Explanations of the causes of war fall roughly into two schools: those arguing for the primacy of environment and technology, and those arguing for the primacy of sociopolitical factors. We re-examine two hypotheses from the former school, viz, societies are more likely to engage in war when they have: 1) more productive subsistence technology; and 2) higher population density. Using data from the Standard Cross-Cultural Sample, and up-to-date multivariate modeling methods, we find only qualified support for the first hypothesis and find the reverse relationship for the second: higher population densities lead to less war, not more. We show that omitted variable bias can explain the failure of previous studies to discover this relationship. Finally, we show that the two schools seem to be equally correct, in that each explains about the same proportion of the variation in frequency of external war.