If Saddam Hussein were actually to deploy his weapons of mass destruction against the United States or its allies, there would be little moral hesitation on the part of American citizens and the leaders of Western Europe. They would throw their whole-hearted support behind a military effort to topple the Bully of Baghdad.

But absent such an outright attack, some Christians argue, America has no warrant to attack Iraq. Indeed, a pre-emptive strike would violate Jesus' teaching in the second great commandment: "Thou shalt love thy neighbor as thyself."

President Bush has our profound sympathy and fervent prayers. A world war in the 21st century could topple civilization. No one with children, spouses, siblings, or parents of military age wants to offer them up to the war gods of commerce, energy sources, or political reputation. Nevertheless, the Christian tradition may not prohibit a pre-emptive strike in all circumstances. If all other requirements of just-war teaching are in place, such a strike could become a duty.

The just-war tradition is not merely a checklist of requirements to meet before undertaking military action: just cause, proportional use of force, no direct attack on civilians, etc. Instead, Christian just-war theology is a positive theory of domestic governance and international relations. Both George Weigel, author of Tranquillitas Ordinis, and the late Christian ethicist Paul Ramsey of Princeton have argued eloquently for this constructive understanding.

Ramsey demonstrated that when Christianity entered the Constantinian era, Augustine and Ambrose applied Jesus' command to love our neighbors to the responsibilities of government. It would be illegitimate (as Jesus taught in the Sermon on the Mount) for an ...