There has been a lot of talk of two camps of Catholics, one that is opposed to the war in Iraq and one that supports it. In fact there is a lot of unity on the question of a U.S. invasion of Iraq: The Pope, bishops around the world, and, it would seem, most of the world's Catholics oppose the war.

Especially in the United States, however, many Catholics have reasoned, thoughtful opinions which differ from the prevailing view of Catholic thought. This is their prerogative. After all, judging the moral legitimacy of military action “belongs to the prudential judgment of those who have responsibility for the common good,” teaches the Catechism of the Catholic Church (No. 2309). The hierarchy won't make that judgment for the civil authorities, nor should it. American Catholics needn't choose between the president and the Pope.

But that doesn't mean Catholics can simply ignore what the Vatican is saying about the war. Quite the contrary. While the magisterium of the Catholic Church doesn't tell us which wars are just and unjust, it does teach clearly against unjustly waging war.

It comes in the Catechism under the fifth commandment: “Thou shall not kill.” War is not an exception to the fifth commandment — on the part of an unjust aggressor, it is a particularly egregious violation of the fifth commandment. By going to war unjustly, an aggressor sets off an abhorrent chain of death, destruction and woe.

“Because of the evils and injustices that accompany all war,” says the Catechism (No. 2307), “the Church insistently urges everyone to prayer and to action so that the divine Goodness may free us from the ancient bondage of war.”

War does bring evil. Those in a war-torn country lose either their lives or their way of life, and they don't get to pick which. They may lose their families. They often lose their minds. War maims children. It maims soldiers. It fills peoples' minds with memories of death and fills soldiers' minds with memories of killing. It changes everything it touches, and it touches everything.

Nonetheless, military aggression is sometimes necessary — most notably, as a means of self-defense.

“The legitimate defense of persons and societies is not an exception to the prohibition against the murder of the innocent that constitutes intentional killing,” says the Catechism.

Cardinal Joseph Ratzinger explained in 2001 why the U.S.-led action in Afghanistan didn't violate the “do not kill” rule: “The father of a family who sees his own attacked has the duty to do everything possible to defend the family, the lives of persons entrusted to him, including, if need be, with proportional violence.”

Other Vatican officials agreed that Operation Freedom was a just war.

Just as killing the man who is trying to murder your family makes you a hero, not a murderer, defending your nation is a duty, not a sin.

But the converse is also true. If you intentionally kill when you don't need to do so, it is murder. And if you go to war when you don't need to do, it is gravely wrong — not for the troops, but for the ones who send the troops in.

No, the Church doesn't demand we believe that war against Iraq is wrong. But if we are Catholics, we will believe, with all our hearts, the principle that it is wrong to go to war unjustly. When a war is proposed by our nation, we will listen very carefully to what the voices of our Church say about that war.

The Vatican's position is not the extreme position of some who oppose the war. John Paul doesn't put President Bush and Saddam Hussein on the same level. The message a Vatican delegate brought to Saddam was simple: Disarm; don't bring evil onto your own country. So was the message to Bush: There are still peaceful avenues to seek to disarm Iraq.

What we are witnessing is our Holy Father doing what the Catechism tells us all to do, in No. 2708: “All citizens and all governments are obliged to work for the avoidance of war.”