It is an enormously delicate subject. Catholicism has always rejected pacifism as incompatible with the demands of justice, but in the face of the horrors of modern warfare, a certain practical, if not doctrinal, pacifism has taken hold. Hence the vigourous campaign of the Holy See against not only the Iraq War in 2003, but also the Gulf War in 1991, when it was impossible to deny that an unjust aggressor could only be repelled by armed force.

Yet the same pope who led those intense campaigns enunciated the case for war under the name of “humanitarian intervention” in his World Day of Peace Message of Jan. 1, 2000.  

“An offense against human rights is an offense against the conscience of humanity as such, an offense against humanity itself,” wrote the Venerable John Paul II. “The duty of protecting these rights therefore extends beyond the geographical and political borders within which they are violated. Crimes against humanity cannot be considered an internal affair of a nation.”

That principle dealt with the objection that a nation could not use armed force against another nation unless it was the target of that aggression. But John Paul went further still.

“Clearly, when a civilian population risks being overcome by the attacks of an unjust aggressor and political efforts and non-violent defence prove to be of no avail, it is legitimate and even obligatory to take concrete measures to disarm the aggressor,” the late Holy Father wrote. “These measures however must be limited in time and precise in their aims. They must be carried out in full respect for international law, guaranteed by an authority that is internationally recognized and, in any event, never left to the outcome of armed intervention alone.”

That is not cheerleading for war by any means. Yet it speaks of “obligatory” measures to disarm the aggressor. That means war is sometimes necessary, even if it is to be avoided by recourse to other means first.

The experience of the Rwandan genocide and the Balkan massacres in the mid-1990s led John Paul to raise his voice for armed humanitarian intervention. Canadians know this story well, for it was Lloyd Axworthy, our foreign minister from 1996-2000, who articulated a “responsibility to protect” — the doctrine by which the international community has an obligation to intervene to prevent precisely what was being done by Gadhafi to his own people. It is the diplomatic equivalent of John Paul’s moral argument.

This rationale for war needs further moral and diplomatic development. To begin with, who bears this responsibility? The United Nations security council, with vetos held by China and Russia? The European Union? NATO? The Organization of American States? The African Union? The Arab League? The Commonwealth? La Francophonie? If there is a moral obligation, it must fall upon someone to discharge it. In Libya it was thought critically important that the Arab League called for armed intervention. But why should a motley collection of morally odious regimes be custodians of this moral responsibility, to be discharged largely by liberal democracies across the sea?

Even more provocatively, does the moral duty of armed humanitarian interventions mean that states are morally obliged to maintain military force sufficient to discharge this duty? The Arab League called for military force, along with the British and the French. Why then are the Americans actually waging the war? It’s clear that they alone have sufficient military might. But does that mean that Britain, France and Canada, for example, are morally negligent in not maintaining sufficient military power to carry out the responsibility to protect?

The questions raised by the moral duty of humanitarian intervention were raised by Pope John Paul, but not answered by him. The Church’s ancient just war tradition has deep theological resources to develop these answers, but has not yet done so. That work needs urgently to begin.