In the ongoing argument between foreign policy realists and
idealists, the just-war tradition of moral reasoning about the use of
force has played a crucial mediating role for centuries. Rooted in
the conviction that all human action--even in the distinctive field
of international affairs, and even in the extremity of war--is
susceptible to moral scrutiny and judgment, the just-war tradition
has insisted that moralists take a realistic account of politics as
an arena of conflict in which the quest for justice and peace is
inevitably fraught with ambiguity and disagreement. Its mediation has
also enabled statesmen to maintain an accepted role for moral
judgment in the very domain--that of war--farthest from the regular
application of human compassion, law, and comity. Just-war theory
has, in short, been a civilized and civilizing agent in the darkest
corners of the human social endeavor, and it has kept the church from
straying too far from the realm of this world.

The ancient question--How can the use of force serve just ends?--that
has been the centerpiece of Christian reflection on just war from the
fifth century has lost none of its urgency today. Indeed, post-Cold
War international politics offers a fertile field for reflection by
moral philosophers and statesmen alike, as the world stands on the
edge of the third millennium of the common era. With the fear of and
focus on superpower nuclear tensions now subsided, world politics
offers situation after situation in which one can imagine the use of
proportionate and discriminate force serving just and prudential ends.

Yet, as in other disciplines and sub-disciplines that treat such
matters, just-war theorists often find themselves at sea today. The
reason, however, has less to do with the confusions of the post-Cold
War world or the classic canons of just-war thinking than with the
intellectual deterioration of that theory itself in influential
quarters. Precisely when statesmen might well look to just-war theory
for guidance on the always-tangled questions of relating appropriate
means to desirable ends, many contemporary just-war theorists are
engaged in a process of self-marginalization. Pressed by the
experience of two world wars and the special circumstances of the
nuclear age, and tempted by secular ideological notions, these
theorists have altered the very ground on which the theory itself has
stood for more than a thousand years. While the core of just-war
tradition is based on opposition to injustice, the recent metathesis
is based instead on a "presumption against war"--a very different
matter indeed.

The burden of this essay is to trace briefly the essential elements
and philosophical bedrock of just-war theory, and to show how it has
changed over the last century--and especially over the past three
decades. I argue that recent changes reflect contingent judgments on
the nature of modern war that do not match the character of
contemporary armed conflicts. I conclude by suggesting that, in its
original form, just-war theory remains relevant to the challenges
faced by statesmen today. I illustrate this relevance by identifying
several contemporary policy implications that follow from
understanding the just-war idea as aimed against injustice rather
than against the use of force itself.

The Classic Just-War Idea

The just-war tradition addresses two issues regarding the morality of
the use of force: when it is right to resort to armed force, and what
it is right to do when using force--jus ad bellum and jus in bello,
respectively. While these two issues are related, the question of
permissibility has priority, for absent the determination that a use
of force is morally justified, even the most strictly delimited means
are, in terms of the just-war tradition, unjust.

The requirements of jus ad bellum are clear in the theory, especially
as developed by Thomas Aquinas in the thirteenth century. Above all,
the resort to force must have a just cause. It must also be
authorized by a competent authority, and it must be motivated by the
right intention. And it must pass four prudential tests: that it be
expected to produce a preponderance of good over evil; that it have a
reasonable chance of success; that it be a last resort; and that its
expected outcome establish peace. Some commentators add that a just
war must also be formally declared, but most agree that the first
three requirements subsume this one as well.

The requirements of jus in bello are also clear. The use of force
must be discriminate (it must distinguish the guilty from the
innocent), and it must be proportional (it must distinguish necessary
force from gratuitous force).

A study of the just-war tradition suggests that, above all, the first
requirement of jus ad bellum--that it have a just cause as a response
to injustice--is the font of the entire tradition. This becomes
obvious if we examine several benchmark figures in the evolution of
just-war theory.

The origins of a specifically Christian tradition on just war are to
be found in the thought of Augustine and his mentor, Ambrose of
Milan, in the fourth and fifth centuries. They inherited--and did not
challenge--a Christian consensus that the example and teaching of
Jesus required that Christians not defend themselves when attacked
but should instead turn the other cheek when confronted with
violence. But first Ambrose and then Augustine reasoned that the
prohibition of self-defense did not imply that a Christian might not
defend his neighbor when attacked. On the contrary, they argued, it
is a duty of Christian love to defend the innocent in such
circumstances. Not providing such defense is itself morally wrong: as
Ambrose wrote in first advancing his insight, "He who does not keep
harm off a friend, if he can, is as much in fault as he who causes
it." Augustine concurred and expanded the point.

Clearly, Ambrose and Augustine began with the duty of love to protect
the innocent, not with a presumption against doing harm, even to an
enemy. They reasoned that the duty to protect the innocent permitted
use of force against the wrongful attacker up to the level needed to
prevent the attack from succeeding, though it must not exceed this
level, since the evildoer is himself considered to be someone for
whom Christ died. Thus the consideration of restraint in the use of
force arises only after the duty to use force is recognized, and
restraint follows not from a presumption against harm but from the
same duty of love directed toward the evildoer.

The logic of this position was in turn developed by the medieval
heirs of these early figures, beginning with Gratian and other
canonists in the twelfth and thirteenth centuries. But in retrospect,
the position of Thomas Aquinas looms as especially important, both
because of his general influence on later Catholic thought and
because of his dependence on Augustine himself in the matter of
just-war theory.

In order for a war to be just, Thomas Aquinas wrote, three things are
necessary, namely: sovereign authority, just cause, and right
intention. Since we are particularly interested in the conditions
that justify resort to force, it is useful to look first at how
Thomas (citing Augustine) defined just cause:

"[J]ust cause is required, namely that those who are attacked, should
be attacked because they deserve it on account of some fault.
Wherefore Augustine says: A just war is wont to be described as one
that avenges wrongs, when a nation or state has to be punished for
refusing to make amends for the wrongs inflicted by its subjects, or
to restore what has been seized unjustly."

This focus is also clear in Thomas' discussion of the requirement of
sovereign authority for a just war. Defining this requirement he
cites a text frequently quoted in medieval writing on the ethics of
war, Romans 13:4: "The sovereign beareth not the sword in vain: for
he is God's minister, an avenger to execute wrath upon him that doth
evil." Thomas continues, "so too, it is [a sovereign's] business to
have recourse to the sword in defending the common weal against
external enemies."

That the resort to force in itself is not the moral problem here is
all the more clear when Thomas turns to the requirement of right
intention for a just war, again quoting Augustine:

"True religion looks upon as peaceful those wars that are waged not
for motives of aggrandizement, or cruelty, but with the object of
securing peace, of punishing evil-doers, and of uplifting the good."

What is morally condemnable in war, Thomas continues, is not force
itself but the use of force with the wrong intention, namely "[t]he
passion for inflicting harm, the cruel thirst for vengeance, an
unpacific and relentless spirit, the fever of revolt, the lust of
power, and such like things." As for the argument that prudential
considerations may overrule the presence of just cause, Thomas leaves
judgment to the sovereign; it is not a matter for the Church to
determine, and certainly not to determine in advance for all war.

Moving forward from the medieval base into the modern period, two
other benchmark figures, Francisco de Vitoria (1492-1546) and Hugo
Grotius (1583-1645), illustrate the essential continuity of this
conception of just war. They did, however, introduce two changes made
necessary by the modern period. In medieval times, the just-war
tradition applied only to wars between Christians, not between
Christians and non-Christians (notably Muslims), and, theologically
speaking, Western Christianity was still monolithic. With the Spanish
expansion into the new world there arose the question of the
propriety of colonial wars against non-Christian peoples, and then
came the dilemmas occasioned by the Protestant Reformation. The first
change introduced by Vitoria and solidified by Grotius was to locate
the justifying causes for war squarely within natural law and the law
of nations, thereby ruling out appeals to religion (or other
ideological causes) as justifying resort to war. The second was the
recognition that in a given conflict both sides might appear to have
just cause.