As America turns to God for guidance and strength in the war on terrorism, its actions must be shaped by God's rules for when and how military action may be taken -- what Catholic theology calls just war doctrine. It is important that ordinary citizens be informed about these rules so they can help inform our leaders at key junctures through the democratic process.

In the Beatitudes, Jesus tells us "blessed are the peacemakers" (Matt. 5:9). Elsewhere in the Sermon on the Mount he tells us "if any one strikes you on the right cheek, turn to him the other also" (Matt. 5:39). From such verses some have concluded that Christianity is a pacifist religion and that violence is never permitted.

But the same Jesus elsewhere acknowledges the legitimate use of force, telling the apostles, "let him who has no sword sell his mantle and buy one" (Luke 22:36). How are these passages to be reconciled?

In broad terms, Christians must not love violence. They must promote peace whenever possible and be slow to resort to the use of arms. But they must not be afraid to do so when it is called for. Evil must not be allowed to remain unchecked.

Added weight is given to this realization when one recognizes that Scripture -- all of Scripture -- is inspired by God (2 Tim. 3:16). This means that the Old Testament is just as inspired as the New Testament and thus an expression of the will of Christ.

The Old Testament acknowledges frankly that there is "a time to kill" (Eccles. 3:3). At various times in the Old Testament, God commanded the Israelites to defend their nation by force of arms. Yet it was always with the recognition that peace is the goal to be worked for. Thus the psalmist exclaims, "how good and pleasant it is when brothers dwell in unity!" (Ps. 133:1). Peace is the goal, but when it cannot be achieved without force, force must be used.

In the same way, the New Testament sets forth the goal of peace but acknowledges the legitimate use of force. It does so by John the Baptist's acknowledgment that Roman soldiers, whose job it was to enforce the Pax Romana, or "Peace of Rome," could keep their jobs (Luke 3:14) and by Paul's observation that the state "does not bear the sword in vain" but is "God's servant for your good" (Rom. 13:4).

As long as Christianity remained a minority religion in the Roman Empire, it was not forced to put these insights together into a formal theory of when warfare could be used. But as Christianity grew predominant, more attention had to be devoted to this subject. By the time of Augustine (A.D. 354-430) the need for a theory of when warfare was just was keen, and Augustine provided one, crystallizing biblical principles into what is now known as just war doctrine. In the intervening centuries the theory has been refined, but its framework remains as he gave it.

The most authoritative and up-to-date expression of just war doctrine is found in paragraph 2309 of the Catechism of the Catholic Church. It says:

The strict conditions for legitimate defense by military force require rigorous consideration. The gravity of such a decision makes it subject to rigorous conditions of moral legitimacy. At one and the same time:

1.     the damage inflicted by the aggressor on the nation or community of nations must be lasting, grave, and certain;
2.    all other means of putting an end to it must have been shown to be impractical or ineffective;
3.     there must be serious prospects of success;
4.     the use of arms must not produce evils and disorders graver than the evil to be eliminated. The power of modern means of destruction weighs very heavily in evaluating this condition.

These are the traditional elements enumerated in what is called the "just war" doctrine. The evaluation of these conditions for moral legitimacy belongs to the prudential judgment of those who have responsibility for the common good.


The strict conditions for legitimate defense by military force require rigorous consideration. The gravity of such a decision makes it subject to rigorous conditions of moral legitimacy. At one and the same time . . .

Here the Catechism indicates the gravity of the decision to go to war. Before this can be done "rigorous consideration" must be given to whether the following conditions are met. It is not enough for just some of them to be met. Instead, all must be met "at one and the same time."

The damage inflicted by the aggressor on the nation or community of nations must be lasting, grave, and certain.

The first condition indicates that there must be an aggressor who is harming the nation or the community of nations. One cannot go to war simply to expand one's sphere of influence, conquer new territory, subjugate peoples, or obtain wealth. One only can go to war to counter aggression.

In recent wars, the aggressor often has been a nation-state, such as Germany was in the First and Second World Wars. But nation-states are relatively new in world history. Throughout much of history the aggressors were much smaller and more loosely organized. Even today many small wars are fought between tribes. In recent years they have been fought between national armies and drug cartels. And in the war on terrorism a principal aggressor has been the terrorist organization al Qaeda.

The damage inflicted by the aggressor must be "lasting, grave, and certain", An aggression that is temporary and mild would not meet this condition. It must be foreseen to have effects that are both lasting and grave.

It also must be foreseen with moral certainty, moral certainty being the highest kind of assurance that is possible in geo-political matters. If this is present -- and if the other conditions are met -- then it is lawful to resort to war.

This means that it is not necessary for the aggressor to strike first. A moral certainty that the aggression will occur is sufficient. Such certainty might be present, for instance, if a party with a history of aggression began amassing troops or munitions.

In a world where it is possible for an aggressor to strike at a distance, with little or no warning, and to cause mass casualties, it is important to identify a potential aggressor early and determine whether he poses a morally certain danger.

All other means of putting an end to it must have been shown to be impractical or ineffective.

The second condition establishes war as a last resort. If there are other practical and effective means of stopping the aggressor, they must be used.

Alternatives include one-to-one diplomacy; international pressure; economic sanctions; and such tools as blockades, quarantines, covert actions, and small-scale raids that do not amount to a full-scale war effort. It is not necessary to employ all such methods before going to war. It is sufficient if rigorous consideration reveals them to be impractical or ineffective.

They would be shown to be impractical if rigorous consideration revealed that, even though they might work in theory, they were not practically possible.

They would be shown to be ineffective if they had little or no chance of stopping the aggression and preventing the damage that it will bring.

There must be serious prospects of success.

The third condition is that the war must have "serious prospects of success."

It is not possible to have a guarantee of success. Even nations with overwhelming military force can lose wars to less well-armed nations, as happened to the U.S. in the Vietnam War. This may be caused by a loss of public will, by lack of expertise in fighting a particular conflict, the intervention of other nations, the outbreak of side conflicts, or other factors.

Because it is impossible to guarantee the outcome of an event as chaotic and destabilizing as war, all that is required for this condition is that there be a substantial possibility of success.

The use of arms must not produce evils and disorders graver than the evil to be eliminated. The power of modern means of destruction weighs very heavily in evaluating this condition.

The final condition has to do with the foreseen consequences of the war. Even if a victory can be foreseen, the damage that is done by the war itself must be taken into account.

As the Catechism notes, the weapons of mass destruction that are available to many nations play a large part in evaluating whether this condition is met. Armed with these weapons, it would be possible for nations to use excessive destructive force when stopping an aggressor, resulting in more casualties than would have occurred if the aggression had been allowed to run its course. In some measure, the evaluation of this condition pertains to the question of how the war is conducted, which will be dealt with below.

Wars inescapably cause damage. This includes the collateral damage they produce in civilian casualties. They also can create other evils, such as destabilizing neighboring countries, changing international alliances in harmful ways, and creating economic burdens.

It is incumbent on those making the decision to go to war to attempt to the best of their ability to foresee both what damage will result if the war is conducted and what damage will result if it is not. The former must not clearly outweigh the latter.

The evaluation of these conditions for moral legitimacy belongs to the prudential judgment of those who have responsibility for the common good.

Finally, the Catechism identifies those who have the burden of evaluating the conditions for whether a particular war is just: "those who have responsibility for the common good." In modern nation-states, this means the government.

Governments are privy to information gathered by intelligence services and other means that the general public does not possess. Because the public is not in possession of this information, the public is not in as advantaged a position to determine whether the conditions are met. As a result, the public must in significant measure be prepared to trust its leaders to make the right decision.

There may not be a guarantee that the government will do so, but, except in the case of fundamentally evil regimes, it is more likely that the government would arrive at an appropriate course of action than would the general public.

This is not to say that the public has no voice in such matters. Particularly in democracies, it does. The public elects its leaders and, through public debate, helps guide its leaders' decisions. Nevertheless, the general public does not bear ultimate responsibility for the decision to go to war. That belongs "to the prudential judgment" of its political leaders. They must evaluate the situation and make their best judgment whether the conditions for just war have been fulfilled.

Once the decision to go to war has been reached, a new set of issues is placed in focus. These have to do with how the war is conducted. Thus the Catechism states:

The Church and human reason both assert the permanent validity of the moral law during armed conflict. The mere fact that war has regrettably broken out does not mean that everything becomes licit between the warring parties (CCC 2312).

A particular danger in wartime is brutality toward those not engaged in combat. Frequently in the history of warfare, soldiers have maimed, raped, and even killed those who did not pose a physical threat to them. Sometimes this has escalated into genocide. The Catechism is at pains to stress the moral illegitimacy of all of these:

Non-combatants, wounded soldiers, and prisoners must be respected and treated humanely. Actions deliberately contrary to the law of nations and to its universal principles are crimes, as are the orders that command such actions. Blind obedience does not suffice to excuse those who carry them out. Thus the extermination of a people, nation, or ethnic minority must be condemned as a mortal sin. One is morally bound to resist orders that command genocide (CCC 2313).

Unlike many countries, America has a strong commitment to this principle. The U.S. is famous for its humane treatment of non-combatants, wounded soldiers, and prisoners of war. Indeed, America is renowned for turning former wartime enemies -- such as Germany, Japan, and Italy -- into friends.

The treatment of non-hostile individuals in wartime is not the only consideration involved in the just prosecution of a war. The existence of weapons of mass destruction poses special moral challenges. In this regard the Catechism states:

Every act of war directed to the indiscriminate destruction of whole cities or vast areas with their inhabitants is a crime against God and man, which merits firm and unequivocal condemnation. A danger of modern warfare is that it provides the opportunity to those who possess modern scientific weapons -- especially atomic, biological, or chemical weapons -- to commit such crimes (CCC 2314).

The U.S. has not always been committed to this principle. In the Civil War, World War I, and World War II the United States violated it. Grave violations during World War II included the firebombing of Dresden and the atomic bombings of Hiroshima and Nagasaki.

These were not attacks designed to destroy targets of military value while sparing civilian populations. They were deliberate attempts to put pressure on enemy governments by attacking non-combatants. As a result, they were grave violations of God's law, according to which, "the direct and voluntary killing of an innocent human being is always gravely immoral" (John Paul II, Evangelium Vitae 57).

It is important to recognize what this principle does and does not require. While it does require strenuous efforts to avoid harming innocents, it does not require the result of no innocents being harmed. Such a result is impossible to guarantee. Even with the smartest of smart munitions, it is not possible to ensure that no non-combatants will be harmed in wartime. As tragic as it is, collateral damage to innocents is an inescapable consequence of war. Catholic theology recognizes this. It applies to such situations a well-established principle known as the law of double-effect. According to this law it is permissible to undertake an action which has two effects, one good and one evil, provided that certain conditions are met.

Although these conditions can be formulated in different ways, they may be enumerated as follows: (1) the action itself must not be intrinsically evil; (2) the evil effect must not be an end in itself or a means to accomplishing the good effect (in other words, it must be a foreseen but undesired side-effect of the action); and (3) the evil effect must not outweigh the good effect. If these three conditions are met, the action may be taken in spite of the foreseen damage it will do.

The law of double-effect would not have applied to the cases of Dresden, Hiroshima, and Nagasaki. In these situations though the act (dropping bombs) was not intrinsically evil and though it is arguable that in the long run more lives were saved than lost, the second condition was violated because the death of innocents was used as a means to achieve the good of the war's end.

Fortunately, despite these past, grave transgressions, the United States is now committed to the principle of sparing innocent life during military actions. It has repeatedly and sincerely expressed its intent to minimize civilian casualties and to serve as a liberator of captive populations in the War on Terrorism. The U.S. is now committed to the principles of the just war.

As the Second Vatican Council noted, "insofar as men are sinful, the threat of war hangs over them, and hang over them it will until the return of Christ" (Gaudium et Spes 78). The danger of war will never be completely removed prior to the Second Coming.

Christ's followers must be willing to meet this challenge. They must be willing to wage war when it is just and they must be willing to wage it in a just manner.

Simultaneously, they must work to establish a just and peaceful order among the nations. In so doing they seek to fulfill the words of the prophet, according to which the nations "shall beat their swords into plowshares, and their spears into pruning hooks; nation shall not lift up sword against nation, neither shall they learn war any more" (Is. 2:4).