Divided Armies Inequality and Battlefield Performance in Modern War Lyall Jason

Divided Armies is a ground-breaking work of social science and military history. Among many contributions, Divided Armies should have enduring influence in the study of international affairs for three reasons. First, by introducing the Project Mars dataset, Jason Lyall (2020b) contributes mightily to addressing selection bias in the study of war, which has long focused on Western states and armies. Replications, robustness tests, and extensions of his work using his transparent and public data will enrich future research. Second, the exhaustive, multi-method analysis of the drivers of battlefield performance in modern war is innovative and enlightening – Lyall’s connection of first-rate quantitative analysis with deep military history is unique. Finally, the finding that “meaningful inclusion creates lethal armies; military inequality divides them, destroying them from within (2020a, 431)” should shape how scholars understand war, but also how states treat their citizens as a matter of national security.