Deservedly or not, critics sometimes caricature just war thinking as jingoism or (increasingly) pacifism by another name—in other words, they portray just war as a kind of foreign policy: either interventionist or non-interventionist. This is a fundamental misunderstanding of the tradition of just war thought. Just war thinking is moral analysis of military action, not a framework for foreign policy. Acknowledging these limitations helps us to become better just war casuists, and it highlights the need for values-driven strategic thinking in the foreign policy sphere.

Historically, just war thinking developed as a moral restraint on warfare, rather than as a formula to determine whether or not a state goes to war. In other words, one cannot take two parts just cause, one part legitimate authority, and one part prudence, stir, and alchemize a policy decision to launch a military engagement with a foreign power.

From ancient times, warfare has been a prerogative of sovereignty, and legitimate reasons for going to war ranged from a desire for resources to revenge for insults or injury to the sovereign or state. With a nod to Carl von Clausewitz, war was an instrument of state policy.

As Christianity’s influence spread through the Roman Empire and its successor states, just war thinkers argued (with varying degrees of success) that because there is a prima facie moral prohibition on taking human life, morally defensible war was limited to campaigns to uphold the cause of justice—itself the moral justification for a state monopoly on the use of violence.

Some commentators contend that just war thinking betrayed early Christianity’s pacifism. It is perhaps more accurate to note that thinking about the morality of warfare only becomes salient when a culture can wage war successfully, or when its moralists can influence state policy about war. As Michael Walzer has described, for centuries Judaism said little about the morality of warfare, because there was no Jewish state to defend. Similarly, Christianity did not focus ethical reflection on warfare until those in charge of warmaking were likewise Christian.

We see similar trends in thinking about war in our own era. Post-World War II just war thinking unfolded against the backdrop of the American-led liberal international order, when American military capability meant debate about war focused more on morality than prudence or strategy. Others distinguished between “wars of necessity” or “wars of choice”—the realist version of just cause. In either case, since the Vietnam War, moral concern revolved primarily around the restraint of American power, a classic application of just war thought.

Following the 2021 US withdrawal from Afghanistan ending America’s longest foreign war, two threats to the community of liberal states (and therefore to US interests and values) are on the immediate horizon: China’s ambitions in the South China Sea (particularly in Taiwan), and Russia’s aggression toward Ukraine. Both challenge the post-Cold War balance of power along the borders between the liberal international community and globally influential authoritarian states.

Though not formal treaty partners with the US, open hostilities in either of these cases could provide just cause for the US and its allies to initiate a military response. Likewise, the concept of jus post bellum supported leaving an open-ended US presence in Afghanistan, to prevent what is now happening there—widespread starvation, the casting of women out of public life, and a return to the repression, corruption, and violence of Taliban rule.

But to paraphrase St. Paul, something may be permissible without being beneficial. Globally, there are many just causes for military intervention: to defend northern Nigerians from religious and ethnic terror, to settle the violence in Tigray, to liberate the Uighurs, to overthrow the North Korean regime, and so on. But as the current (non-) response to each of these cases shows, while just war thinking is necessary to determine whether or not a military response would be morally justified, it is not sufficient to guide policy in a world of potential conflagration.

The cases of China and Russia in particular raise a key question for foreign policy thinkers: When it comes to the increasing boldness of authoritarian powers on the world stage, how should we respond? Are we aiming at cooperation, containment, détente? What price will we pay to avoid conflict? Are we willing to accept democratic nations falling under the grip of authoritarianism? In other words, what is freedom worth?

In this potentially post-liberal era of international relations, circumstances may force some uncomfortable answers—and they will not be found at the end of a checklist or formula. For just war thinking to be other than what its critics suggest, it must be linked to a foreign policy that itself can be defended on moral grounds.

Acknowledging this point, recent work from Christian realist thinkers engages the conversation around foreign policy, grand strategy, and the rules-based liberal international order. Readers looking for more in-depth examinations of these questions can peruse books from Providence contributors Robert Joustra, Paul D. Miller, and Eric Patterson, each of whom approaches these ideas from the perspective of their own theological commitments as well as from within the broader tradition of Christian realism.

Political theorist Jean Bethke Elshtain was fond of a line she adapted from Hannah Arendt: “Politics is not the nursery.” By this, she usually meant something along the lines of, in a world containing both petty villains and real evil, it takes mental and moral fortitude to act responsibly on behalf of one’s political community. At its best, just war thinking embodies these qualities—qualities that should characterize all our actions on the global stage.