The just war tradition was born in the Middle Ages as a way of thinking about the use of military force as a manifestation of sovereign responsibility. Emerging from the philosophical patrimony of both ancient Israel and the Greco-Roman worlds, the most significant early Christian expression of just war theory originated in Augustine of Hippo. From there it took on a more systematic character only some 800 years later with Gratian’s twelfth century Decretum; following this, it attained theological maturity through Thomas Aquinas in the thirteenth century; and then, deeper still into the Middle Ages, it was enhanced by the influence of the ideas and practices of the chivalric code and Roman law, and through continued reflection on the experience and theory of war and government.

For the thinkers in this its classic form, the just war tradition is grounded in a verse from the thirteenth chapter of the letter to the Roman church: “For [the sovereign ruler] is God’s minister to you for good. But if you do evil, be afraid; for he does not bear the sword in vain. He is God’s minister, an avenger to execute wrath on him that does evil.” Paul’s emphasis on the good of government helps signal the just war tradition as essentially eudaemonist – that is, it promotes genuine human flourishing. It accomplishes this through fidelity to the fundamental Christian duty of neighbor love. This principle norm makes a universal anthropological assertion: All human beings, including our enemies, are right objects of love. This is because in the biblical view every human individual is made in the image of God and has a particular call to exercise dominion and participate in the care, and salvation, of the world. From this universal assertion that every human being enjoys equal dignity there issues a consequent universal command: All human beings are to love every other.

The way in which just war promotes the love and flourishing of the neighbor under assault should be quite clear. In order to flourish through properly responding to our created call, human beings need to enjoy those goods which make any such response possible. Most basically, of course, this includes the good of life. Because of this, the primary good for which government exercises responsibility is the provision of basic security characterized by order, justice, and peace without which no degree of human flourishing, including life, can long persevere. These goods correspond directly to the three conditions necessary for a just resort to force: sovereign authority, only the one with final responsibility for the political community has the duty to declare war; just cause, reclamation of what has been wrongly taken, and punishment of evil; and right intention, the achievement of real peace. Thus, the just war tradition insists that a nation’s concern extends beyond one’s narrow national interests to include intervention and rescue of the oppressed. In fact, the just war tradition insists that it is in our national interests to rescue the oppressed. Virtue is a national treasure.

But the exercise of love is good not only for the object of one’s love. The command to love is good, as well, for the one commanded. It is good for us to love our neighbor. One way the just war tradition promotes the flourishing of the just warrior is by assisting in the acquisition of virtue. It is good, genuinely good, to grow in such things as benevolence, courage, justice, mercy, and charity – characterized by other-centered acts of self-donation. This is true even if it should cost one everything, because the Christian has the gospel promise that the faithful will be recovered from death. Meanwhile, the virtues cultivate in the virtuous soul a taste for the character of heaven, even in the sometimes-seeming-hell of war. These virtues promote in the just warrior a disposition toward the just prosecution of war, characterized chiefly by a regard for discrimination – the recognition that we wage war not against all the members of an adversary nation but only against the combatants who remain a martial threat; and by proportionality – the use of force limited to that required to end the martial threat.

But what of the enemy neighbor? Can the just warrior both love and work toward the flourishing of the enemy-neighbor? According to the just war tradition, he can. One way he can is through individual participation in the right intention of the sovereign’s resort to force in the first place. First, the just warrior avoids those things which are evil in war: the desire for cruel harm, lust for vengeance, an unruly and implacable hatred, the desire to dominate others, and the like. Second, the just warrior seeks to help allow for those conditions which permit for the restoration of peaceful relations and, ultimately, reconciliation. Finally, if human flourishing is achieved by responding appropriately to the divine call to participate in the care of the world, to prevent an enemy from doing evil is to restrain them from committing deep, perhaps indelible harms to their own souls and to dull their own taste for heaven.

Without question, all of this is greatly difficult, made harder by the fact of sin. The just war tradition sets limits to when and how we fight in order to help guard against such errors such as believing ourselves to be involved in simple Manichean binaries of good verses evil. It remains a temptation in just war judgments to allow a just cause to become a crusade. The just war tradition is characterized by humility. We are responsible in history for what we do and how we respond to what others do. But our responsibility for history is more limited. While we share in God’s providence by, ourselves, exercising a limited sort of provident care, what we can achieve is always only approximate. We need not strive for perfect peace, perfect justice, perfect order. They are beyond our grasp regardless. But the just war tradition insists we have a role to play is setting or allowing to be set those conditions which allow for the cultivation in history of either hells on earth or for bearable living, even flourishing.

There is much more to be said, of course. And so it shall be. Stay Tuned.

Marc LiVecche, PhD, is managing editor of Providence and the Scholar of Christian Ethics, War, & Peace at the Institute on Religion and Democracy.

Image: Tiffany Window of St Augustine – Lightner Museum (detail) Wikimedia commons