An Ancient Teaching:
The Catholic Church’s teaching on just war developed very early. St. Augustine of Hippo (354-430) was the first Christian writer to describe the four conditions that must be met in order for a war to be just, but the roots of just-war theory go back even to non-Christian Romans, particularly the Roman orator Cicero.
Two Types of Justice Concerning War:
The Catholic Church distinguishes between two types of justice concerning war: jus ad bellum and jus in bello. Most of the time, when people discuss just-war theory, they mean jus ad bellum (justice before the war)—the four conditions by which we determine whether a war is just before we go to war. Jus in bello (justice during the war) refers to how the war is conducted once it has started. It is possible for a country to fight a war that is just, and yet to fight it unjustly—by, for example, targeting innocent people in the enemy’s country.
The Four Conditions for Jus Ad Bellum:
The current Catechism of the Catholic Church (n. 2309) defines the four conditions for determining the justice of a war as:
- the damage inflicted by the aggressor on the nation or community of nations must be lasting, grave, and certain;
- all other means of putting an end to it must have been shown to be impractical or ineffective;
- there must be serious prospects of success;
- the use of arms must not produce evils and disorders graver than the evil to be eliminated.
These are hard conditions to fulfill; the Church teaches that war should always be the last resort.
A Matter of Prudence:
That decision is left to the civil authorities: “The evaluation of these conditions for moral legitimacy belongs to the prudential judgment of those who have responsibility for the common good.” In the United States, for instance, that means Congress, which has the power under the Constitution (Article I, Section 8) to declare war, and the President, who can ask Congress for a declaration of war.
When the Catechism states that the decision to go to war is ultimately a prudential judgment, that means that the civil authorities bear the responsibility for making sure that a war is just before they fight it.
The Role of Modern Weaponry:
While the Catechism mentions that “the use of arms must not produce evils and disorders graver than the evil to be eliminated,” it also states that “The power of modern means of destruction weighs very heavily in evaluating this condition.” Here, the Church is concerned about the possible use of nuclear, biological, and chemical weapons, the effects of which, by their very nature, cannot easily be confined to combatants in a war.
The injury or killing of the innocent during war is always forbidden; however, if a bullet goes astray, or an innocent person is killed by a bomb dropped on a military installation, the Church recognizes that these deaths are not intended. With modern weaponry, however, the calculation changes, because governments know that the use of nuclear bombs, for instance, will always kill or injure some who are innocent.
Because of that, the Church warns that the possibility of the use of such weapons must be considered when deciding whether a war is just. In fact, Pope John Paul II suggested that the threshold for a just war has been raised very high by the existence of these weapons of mass destruction, and he is the source of the teaching in the Catechism.
Joseph Cardinal Ratzinger, now Pope Benedict XVI, went even further, telling the Italian Catholic magazine 30 Days in April 2003 that "we must begin asking ourselves whether as things stand, with new weapons that cause destruction that goes well beyond the groups involved in the fight, it is still licit to allow that a 'just war' might exist."
Furthermore, once a war has begun, the use of such weapons may violate jus in bello, meaning that the war is not being fought justly. The temptation for a country that is fighting a just war to use such weapons (and, thus, to act unjustly) is just one reason why the Church teaches that “The power of modern means of destruction weighs very heavily in evaluating” the justice of a war.