What makes an army successful in battle? A few factors come to mind: strength in numbers, tactical acumen, the type of political institutions at home. New technologies, including artificial intelligence, drones, and hypersonic weapons, might also tip the balance. But one of the most important determinants of battlefield performance is consistently overlooked: equality among soldiers, regardless of their ethnicity.
How societies treat their constituent ethnic groups can make the difference between stunning success and crushing defeat once the shooting starts. As I argue in my new book, the last two centuries of warfare show that inclusive armies—meaning that all ethnic groups represented in the military are considered full citizens of the state they are serving—enjoy far greater success than non-inclusive ones. When armies are drawn from marginalized or repressed ethnic groups, by contrast, performance suffers. These divided armies typically spend as much time coercing their own soldiers to