Note: This is the fifth and final article in a series on the Christian just war tradition.

Imagine North Korean dictator Kim Jong Un announces he will finally implement his family’s long-stated objective of unifying the Korean peninsula. To ensure that no one interferes with his invasion of South Korea, he has hidden his nuclear missiles in the tunnels beneath the DMZ. The dictator threatens that these weapons, which can quickly be moved out of the tunnels, will be launched against Seoul, Guam, and Japan if South Korea, the U.S., or any other nation interferes with his plan.

The Western democracies are left with only two options: They can concede to North Korea’s demands and allow the enslavement of millions of people, or they can launch a preemptive nuclear strike using bunker-buster tactical nukes.

What should a Christian leader do? Would it be possible to use nuclear weapons in this situation in a way that aligns with the just war tradition?

It's never moral to use nuclear weapons on civilian targets, such as enemy cities.

Unfortunately, many of us don’t know how to provide a moral answer to these questions. Theological reflection on the use of nuclear weapons has always been lacking within American churches, and such thought tends to focus on apologies for the use of the atomic bombs on Nagasaki and Hiroshima.* Since the end of the Cold War, almost no fresh thinking has been given to the subject at all by the broader evangelical community.

The most thoughtful consideration of nuclear weapons has tended to come from pacifist groups, such as Anabaptists, and others who support complete nuclear abolitionism. They tend to start with the view that nuclear weapons are intrinsically evil and their use objectively immoral, thus making them illegitimate for any use in just warfare.

Less consideration has been given by those of us who begin with the just war tradition and then attempt to explain how (or even if) nuclear arms can fit within a just war framework. In this article, I want to attempt to provide a model for such reflection by applying what we’ve learned in earlier articles in this series to consider under what conditions nuclear weapons might be acceptable.

When would it be morally legitimate to use nukes?

Let’s begin by assuming that the use of nuclear weapons is being considered in a conflict that meets all of the jus ad bellum criteria. That means the weapons would be considered primarily from a jus in bello perspective (the criteria for justly engaging in warfare), and to a lesser extent, from the jus post bellum perspective, (justice after war).

Nuclear weapons can be either tactical or strategic. A tactical nuclear weapon is a nuclear weapon designed for use on a battlefield in military situations, where friendly forces may be in relatively close proximity. A strategic nuclear weapon refers to a nuclear weapon designed to be used on targets in territory far from the battlefield as part of a strategic plan, such as on military bases, weapons factories, or military command centers.

Whether the weapons are tactical or strategic, their use should align with the two primary criteria for just execution of war, discrimination and proportionality.

As we discussed in a previous article in this series, the criterion of discrimination includes two key components, “innocence” and “deliberate attack.” The first rule of just warfare is that we do not target or kill the innocent. Nuclear weapons must therefore never be used to target noncombatants (i.e., women, children, the aged and infirm, etc.).

This is related to the second component of discrimination—“deliberate attack.” While the innocent may be harmed because of our engaging in warfare—such as when civilians are used as “human shields”—it must not be our intention to deliberately attack them. For this reason, nuclear weapons must not be used on civilian targets; enemy cities cannot be targeted for deliberate attack, even in retaliation. As Rebeccah Heinrichs says,

[U]nder no circumstances should the United States target civilian populations. Targeting civilians violates the fundamental principles that define the character of the United States of America and fails to meet the just war criteria jus in bello. Moreover, even from the perspective of cold realism, claiming to target civilian populations and maintaining a force structure designed to do this would likely not serve American interests, for some enemy leaders do not value the lives of their civilian populations the way that the United States does. In fact, it is reasonable to assert that American policymakers value the lives of enemy countries’ civilians more than their dictators do.

This is why Christians who accept both nuclear weapons and the just war tradition should support a nuclear strategy of counterforce targeting (using nuclear weapons only for military targets) rather than countervalue targeting (targeting of an opponent's assets which are of value but not actually a military threat, such as cities and civilian populations). See Heinrich’s article for more on how a counterforce strategy of deterrence is compatible with the just war tradition.

The second major jus in bello criterion is proportionality. As Jean Bethke Elshtain explains, proportionality “requires that the nature of one’s coercive force should be proportional to any injury sustained or planned, and that at whatever minimal force can be used to do the job should be deployed.” In the context of nuclear weapons, this would require that we should not use a high-yield weapon that has significant long-term effects (such as nuclear fallout) if it is possible to achieve the same military objective with conventional weapons.

In addition to these jus in bello criteria, there is a jus post bellum principle we must consider: the effect on the subsequent maintenance of reasonable living conditions and order for the people of the country where the nuclear weapons are used.

Now let’s apply these principles to our original North Korean scenario. Because the nuclear weapons would be used on a military target with few or no civilians in the area, it would likely pass the test of discrimination. Similarly, the criterion of proportionality may be met if the military commanders determine that non-nuclear bombs are unable to destroy the North Korean nuclear missiles.

Likewise, the area around the bombing may be subjected to nuclear fallout, but that would likely be a lesser harm than allowing the North Koreans to launch a nuclear attack.

Conclusion

While the North Korea scenario is a limited and narrow example, it provides an illustration of how Christians can and should apply just war principles to thinking about when the use of nuclear weapons might be appropriate. Nuclear weapons have neither made the just war tradition obsolete, nor added a significant layer of complexity. “Nuclear weapons do represent a novel and terrifying development in the history of international violence,” says just war theorist Robert L. Phillips, “ but as a form of state initiated force they demand the same kind of scrutiny and moral appraisal as any other kind of weapons system.”

Whether the weapons are slingshots or intercontinental ballistic missiles, Christians have inherited a robust tradition and framework to think morally about how warfare should be conducted.

*Because the debate about the use of nuclear weapons involves a significant degree of complexity, I’ve chosen to avoid discussing it in this article. For now I want to focus on future-oriented consideration of nuclear weapons.