In a recent column, I discussed Nigel Biggar's important new book defending just war theory. Though admiring of the author's clarity and erudition, I found his arguments unpersuasive. Instead of encouraging policymakers and citizens to reflect more deeply on whether to go to war, just war thinking ends up providing additional moral and theological justification for militaristic actions the U.S. and Great Britain would be inclined to undertake anyway. I concluded that the book thus inadvertently demonstrates that "just war thinking, even at its very best, is an intellectual, moral, and theological fraud."

In his rejoinder to my column, Biggar responds by listing a handful of British and American military engagements that he considers unjustified when analyzed using just war criteria. That's helpful — though I also think it's revealing that he doesn't list a single conflict from the past 130 years. (There have been an awful lot of wars since the British invaded Zululand in 1879.)

I'm not sure that counts as a successful rebuttal.

But let's leave that aside for the moment. At the end of my column, I promised a follow-up that would examine the religious sources of just war thinking and ask whether it deserves to be considered Christian at all.

On one level, the answer is an obvious yes. Just war theory took shape in the writings of Augustine, Thomas Aquinas, Francisco de Vitoria, Francisco Suárez, and Hugo Grotius — some of the leading thinkers of Christian civilization — and it was championed in the 20th century by two of Christianity's most celebrated intellectuals and apologists, Reinhold Niebuhr and C.S. Lewis.

But that doesn't mean that these thinkers were justified in treating Christianity as compatible with war-making — any more than the choice of Christian popes, kings, and aristocrats to fight the Crusades automatically makes those wars of imperialistic conquest consistent with the teachings of Jesus Christ.

A powerful dissenting tradition of Christian thinking strongly — and to my mind, persuasively — rejects the easy linkage between war and authentic Christianity. For John Howard Yoder, Stanley Hauerwas, and Richard Hays, the Christian acceptance of violence — and the attempt to establish rational criteria to justify it — can be traced to the reign of Constantine the Great (306–337 AD), the first Roman emperor to convert to Christianity.

Up until that time, Christians expected Christ's imminent return, and as members of a marginal, persecuted sect, they gave little thought to the burdens and responsibilities of political rule. But with the Second Coming seemingly delayed for an indefinite duration and the emperor himself now a Christian, the church's status evolved radically and rapidly. First, Christianity was legalized. Then it was declared the official religion of the empire. Finally, by the end of the 4th century, pagan religious worship was banned.

Christians were now in positions of worldly power throughout what was officially a Christian empire. This is what Yoder called the "Constantinian shift," and it led to a profound change in how Christians thought and acted. Whereas many formerly renounced violence, now they fashioned arguments to distinguish between violence that was legitimate and illegitimate, justified and unjustified, with morally right motives and intentions serving as the decisive consideration. As long as a Christian in a position of political or ecclesiastical authority meant well, recourse to violence could be acceptable and compatible with Christian faith. Just war theory grew out of this change in moral orientation.

As I indicated in my original column, I think the attempt to rationalize and moralize warfare — especially when it comes to judging conduct within a war that's already been declared (ius in bello) — has had a salutary influence. It's a very good thing that armies are now expected to use no more force than is necessary to vindicate their causes and that soldiers refrain from intentionally killing civilians. To the extent that these reforms in military conduct can be traced to just war theory, we should be grateful to Constantinian Christianity and its (very long-term) influence on our civilization.

But we should also recognize that the kind of moral calculus about killing that just war theory recommends and exemplifies — especially when it comes to the decision to initiate military action (ius ad bellum) — has no plausible connection to the life and teachings of Jesus Christ.

Christ taught us to love our neighbors — and nowhere does he indicate or imply, as Biggar (following Augustine) claims, that it's possible to express that love in the act of killing them. Christ also taught us to turn the other cheek, to forgive our enemies for their transgressions against us, and to refrain from responding to an attack by taking a perfectly proportional "eye for an eye."

And then there's Christ's willing acceptance of conviction, torture, crucifixion, and death — a chilling indictment of the horrible deficiencies of the worldly order of things and the injustice that so often prevails within it.

To which just warriors everywhere will reply: But the modern United States and Great Britain are far more moral than a provincial outpost of the 1st-century Roman empire!

Indeed they are. But are they different in kind and in the decisive respect? The answer, I think, is no. Human beings still judge poorly in their own cases. They still deceive themselves about their own righteousness. They still fool themselves into believing that their motives and intentions are pure when pride is really what's driving them. And when these traits are amplified into collective (communal, political, national) endeavors, the logic of self-interest becomes overwhelming and inescapable.

Prideful self-regard is woven into the very fabric of our fallen world. In particular cases, an individual can act out of authentic self-abnegating love for another. But as a group? That is nearly always impossible, at least in this vale of tears.

Which is why Christ taught nonviolence — and Christianity should preach pacifism and the renunciation of political rule.

Let me be very clear: I harbor no illusions about the likelihood of establishing peace on earth. On the contrary, like so much of his teaching, Christ's commitment to nonviolence defies the innermost logic of the world, cuts against the grain of human nature, and subverts the self-interested order that governs collective life. (A "Christian nation," strictly speaking, is an oxymoron.)

But Christians should be honest enough to admit that in continuing to exercise political rule, and in fighting, using force, and killing, they are falling far short of the otherworldly purity to which they have been called by the God they profess to worship and revere.

And that brings me back to Biggar.

One of the highlights of his book is a 37-page chapter in which he examines the Battle of the Somme from World War I. In five months of fighting, the battle left 622,221 British and French troops killed, wounded, missing, or taken prisoner — all for the sake of a gain of six miles of territory.

Generations of critics have argued that this makes the Battle of the Somme a case study in the pointless waste of modern warfare, which tramples human dignity in the mud and causes suffering on a scale unimaginable by earlier ages. But not Biggar, who meticulously constructs a dispassionate, logically pristine case for considering the losses suffered to have been proportionate and thus morally justified. It's a tour de force of rational argument.

And measured against properly Christian ideals, it is obscene.

Reason is a powerful tool, one we should respect and rely on as we think through any number of issues. But it's also almost infinitely plastic. Given the right premises, it can justify nearly anything. Which is why you should never trust it entirely with your life — or the lives of others.

By all means, let's argue about war and peace, justice and God. And if, after all the arguments have been made, we're thoroughly convinced of the need to drop bombs and deploy troops, then let's go to war, with as much restraint and humility as we can muster.

But please, let's not make fools of ourselves by imagining that in doing so we have Jesus Christ on our side, nodding and smiling at the slaughter.