The just-war framework neatly distinguishes between jus ad bellum, the criteria that address political leaders' decisions for waging war, and jus in bello, the criteria that address soldiers' conduct during war. Yet developments in the empirical science of civil wars, the U.S. military's recent preference that ground-level soldiers exercise initiative and autonomy, and the wartime experiences of U.S. soldiers fighting in the twenty-first century converge to reveal an unappreciated overlap between jus ad bellum and jus in bello. I examine three firsthand accounts of service in Iraq and Afghanistan to show how military leaders' contingent decisions – insofar as they choose whom to marginalize politically, befriend as allies in combat, and oppose as mortal enemies – are susceptible, theoretically if not yet practically, of jus ad bellum critique. Drawing on the work of Avishai Margalit, Michael Walzer, and James Murphy, I then argue that military designations of friend and foe implicate ethicists, political authorities, and military educators in a network of obligations. Ethicists must discern how to evaluate commanders' political decisions, polities must prepare soldiers for political work, and military educators must teach the relevant scholarship. This argument has significance for regnant conceptions of military expertise and military education. [ABSTRACT FROM AUTHOR]