The morality of war has been debated since men fought with sticks and stones. Combatants have wanted to believe that they were not mere brawlers, but took up arms in the service of right.
The current fighting in Yugoslavia is no exception. The Belgrade government appealed to international legal norms this week in asking the World Court in The Hague, Netherlands, to stop NATO's "merciless and savage bombing of the civilian population." And Western leaders have justified those airstrikes as motivated by moral and humanitarian concerns, not national self-interest.
World Wide Web sites, law school journals, theologians and opinion writers have all weighed in. Though there is much disagreement, a plurality seems to have formed around the idea that the NATO action may have been morally legitimate in its stated aim of stopping "ethnic cleansing" in Kosovo, but it has lost its justification by failing to achieve that aim.
"Not only has NATO's bombardment failed to stop the ethnic and religious `cleansing,' " read a Web site posting under the name of "Imemind," "but the air war also seems to have intensified the problem."
Thinkers since Aristotle and Cicero have pondered whether war may ever be just or necessary, but modern theories can be traced to the early Christian era.
Following the command of Jesus to be peacemakers, early Christians believed that they should not fight in wars. But, regarding themselves as citizens of an eternal spiritual kingdom, they also generally refused to participate in the civil administration of the Roman Empire.
Then in 313, on the eve of a battle, the Emperor Constantine had a dream. He saw a cross and the words, "In this sign you will conquer." After his victory the next day, he converted to Christianity.
With theirs now Rome's official religion, Christians had to rethink their role in the life of a secular state. The most systematic explication came from Augustine of Hippo (356-430), who wrote that the civil state was divinely ordained for the earthly protection and well-being of its citizens, in parallel to the spiritual kingdom that looked after Christian souls.
It followed, according to Augustine, that war could be undertaken when necessary to protect the peace and good order of a society -- but not for "the desire of harming, the cruelty of revenge, the restless and implacable mind, the savageness of revolting, the lust for dominating and similar things."
As the principles have developed, wars must meet seven tests. They must be waged by a legitimate authority, for a just cause and with the intention of securing a just peace. Fighting must be a last resort. The means used to wage the war must be proportionate to the goal and must discriminate among legitimate targets. Finally, there must be a reasonable prospect of achieving the just aim.
Simple as these principles seem, they have given rise to endless interpretation.
Could Christian priests fight, even in a just war? Most commentators thought not, but at the Battle of Hastings in 1066, Bishop Odo of Bayeux took up a mace, not a sword, so that he could kill without shedding blood.
Can Christians fight on Sundays or holy days? Is it unpardonably deceptive to lay ambushes? Thomas Aquinas (1227-1274) sanctioned both practices.
Is it possible to discriminate between fighters and noncombatants in a guerrilla war, where warriors may live among a civilian population and wear civilian clothing? And, in fact, are not civilians often the architects of war and soldiers merely the instruments?
NATO's attack on Yugoslavia has offered new questions for interpretation. Most discussion accepts that prevention of ethnic cleansing in Kosovo is a "just cause" for war.
But some theologians, such as Stanley Hauerwas, a professor at Duke University, scoff that the idea of "just war" makes no more sense than "just adultery."
The Rev. Al Humbrecht of Sacred Heart Cathedral in Washington suggests that if war was ever justifiable, it no longer is.
"With the type of weapons we have today, I think not," he told an interviewer. "In an age when war was hand-to-hand combat, St. Augustine could talk differently than in an age when we use `smart bombs.' "
Others question whether pacifism is an adequate moral stance in the face of evil.
"This war, more than most, confronts Christians with choosing between saying `never again' to war or saying `never again' to ethnic cleansing and genocide," wrote the Rev. Thomas J. Reese in the magazine America. "These are choices we don't like to make."
As the war has unfolded, some writers who have supported other wars question whether this one is really about Kosovo. Conservative columnist Tony Snow quoted the rhetoric of NATO leaders who invoked "the consensus of the international community" and "the need to ensure the viability of NATO."