When the war began in Afghanistan, Defense Secretary Donald Rumsfeld asked a handful of religious leaders to brief him on just-war doctrine. Most of us gave high marks to the administration's efforts to meet just-war standards. I asked, however, the one discordant question: "How would the administration justify a preemptive strike on Iraq?" Without hesitation, Rumsfeld cited the precedent of Israel's attack on an Iraqi nuclear plant in 1981.

One year later, the question is no longer hypothetical. As I write, U.S. forces are massing for war with Iraq. By the time you read this, troops may be in Baghdad. But whatever happens, the morality of a preemptive strike will continue as a hot debate. Last September, the President drew the battle line, boldly declaring preemption as a national policy.

This issue is of particular concern to Christians since we are the heirs of the just-war tradition formulated by Augustine 1,600 years ago. Historically, the doctrine's requirement of just cause has been defined as responding to an attack.

But has terrorism changed the rules? Should the doctrine be "stretched," as just-war expert George Weigel argues? Can a preemptive strike be morally justified?

The first response from the church was negative. U.S. Catholic bishops oppose an attack unless Iraq can be linked to the September 11 terror strikes. One hundred Christian ethicists announced opposition; so did the general secretary of the Middle East Council of Churches. The new Archbishop of Canterbury and Pope John Paul II both expressed reservations.

But I think this reflects too narrow an understanding of just war. Our attitudes may be unduly influenced by Cold War memories. For four decades, the world was kept in relative peace—at least from ...