Those who do Christian ethics are obliged in the seventies to renew their search for an understanding of the conditions that would justify revolutionary resorts to violence (jus ad belum), of the moral limits upon the conduct of insurgency war and, yes, of the permissible limits of counterinsurgency (jus in bello).But, you may object, that is to ignore a chief cause of American involvement in the Vietnam war: President Kennedy was tempted to begin the escalation of U.S. involvement because he had an available “weapons system“ (the Green Berets) and because he trusted a doctrine of counterinsurgency. What's more, you further object, regardless of what we may think about the morality of insurgency or counterinsurgency as such, a chief lesson to be drawn from Vietnam is that, when an industrial power like the United States gets involved in counterinsurgency in a traditional and preindustrial society, disproportionate violence is bound to be done.