Like all good political science propositions, Lyall’s claim that armed forces whose composition reflects severe inequalities between ethnic groups will fare far worse in battle than those whose composition reflects more inclusive social and political structures seems obvious once stated. But it may well now stand as one of the best-established contentions in the field, supported not only by Lyall’s carefully constructed statistical analysis but also by his series of fascinating case studies that cover a range of encounters, some long forgotten, to show how the proposition works in practice. For instance, Lyall dips into the nineteenth-century wars between Russia and Kokand (now part of Uzbekistan) and between Spain and Morocco to demonstrate that schisms within Kokand’s and Morocco’s armies led to their defeat. Lyall’s book represents a welcome mingling of the traditions of quantitative and qualitative political science. He sets a rigorous and imaginative methodological standard that others will struggle to match, in the process raising questions, perhaps unintentionally, about the value of prior quantitative research that has drawn from inferior databases.