(RNS) Lots of people think war is never justified. President Obama is not one of them. While accepting the Nobel Peace Prize in Oslo, Norway not long ago, he invoked “just war” theory.

Theologians and philosophers from Augustine to Thomas Aquinas to men of modernity have wrestled with the balance of war and peace. Most think sometimes you simply have to do it.

So, amidst two inherited wars, Obama summarized “just war” theory as holding that: “war is justified only when certain conditions were met: if it is waged as a last resort or in self-defense; if the force used is proportional; and if, whenever possible, civilians are spared from violence.”

That’s not directly from the “Catechism of the Catholic Church,” but it is close.

And Obama forgot one very important point in Catholic teaching: there must be serious prospects of success.

Therein lies the root of all the argument, the cause of consternation in this country and elsewhere. If insanity is the repetition of a failing act in the hope it will succeed, then you can see where certain hackles might be raised at Obama’s citing “just war” theory while accepting his prize for peace.

He did not go into detail. How could he? The commander-in-chief of the world’s largest arsenal was there — he and I believe — as a man of peace. But, he did not forget he was running some major conflicts, and neither can we.

The president admitted his limitations. He said he did not have answers to the end of war. But he did challenge all of us “to think in new ways about the notions of just war and the imperatives of a just peace.” He called for alternatives to violence, such as economic sanctions. He called for peace based on the rights and dignity of every individual. And he called for individual and national economic security and opportunity.

These may indeed be the answer. But we’re still at war.

If you can’t stand to think about “just war” — admittedly a testosterone-fueled method of problem-solving — then consider Pope Benedict XVI’s 2010 World Day of Peace Message, set for Jan. 1. Benedict’s answer is clear: “If you want to cultivate peace, protect creation.”

Are the two on a collision course? Or are they approaching the same question from opposite ends of the rifle?

Obama speaks from a position of power. He admits his finger is always on the trigger.

Benedict speaks with the voice of the poor, who are usually looking at the business end of the gun.

How can we bring them together? Benedict will defend just war, in a limited way. Obama will agree with the defense of creation, to a point.

Benedict and Obama have different ways of viewing the planet and its foibles. Both want some balance between peace and human dignity. Both present broad policy, not detail.

But, bringing the two views together is more difficult than it may seem. Obama calls for human dignity, but not for the defense of all human life. Benedict calls for a peace that will accept the so-called useless people (born and unborn), but does not always agree with fellow Catholics about how they should be politically defended.

Some say Obama’s Nobel speech was his best ever –“pitch-perfect” is how one commentator put it — and it did not get as much media play as perhaps it deserved. I’ll wager fewer folks will hear or read about Benedict’s World Day of Peace message, the 43rd to come from Rome.

Yet their common bottom-line, take-away message is unmistakable: we’re all in this together, and if we don’t do what’s right for all of us, one way or another we soon won’t be able to do anything for any of us.

(Phyllis Zagano is senior research associate-in-residence at Hofstra University and author of several books in Catholic Studies.)