A Third Nuclear Age Is Upon Us

North Korea’s moves to develop tactical nuclear weapons show that the slope toward a new era is steepening.

A collage of Kim Jong Un and a nuclear bomb exploding
Paul Spella / The Atlantic; Getty

On the brink. That’s how we tend to think of humanity’s predicament during the most dangerous moments of the nuclear era. But as Thomas Schelling, the godfather of nuclear strategy, once pointed out, the phrase is misleading. The nuclear frontier is not “the sharp edge of a cliff where one can stand firmly, look down, and decide whether or not to plunge,” he wrote, but rather “a curved slope that one can stand on with some risk of slipping”—the slope getting steeper and riskier “as one moves toward the chasm.” Now the slope is getting steeper before our eyes.

That’s not just because of the potential for Russian President Vladimir Putin to use nuclear weapons in a desperate effort to avert defeat in Ukraine. It’s also the result of a threat that isn’t making many headlines but that experts are currently concerned about: North Korea’s development of tactical nuclear weapons—less explosive, shorter-range arms designed for use on a battlefield.

North Korea has been pursuing tactical nuclear weapons for many years, but the latest chapter in this story begins in January 2021, when the country’s leader, Kim Jong Un, explicitly pledged to build such weapons. Then came Pyongyang’s April 2022 test of a short-range missile expressly intended to be wielded as a tactical nuke, followed by cryptic June military announcements that some analysts interpreted as an indication that Kim is planning to deploy the weapons to his frontline artillery units. North Korea watchers expect the country to conduct its seventh nuclear test any day now, which would most likely be aimed at further honing small warheads that could be mated with shorter-range missiles.

If those predictions bear out, North Korea’s next nuclear test would herald what some scholars have dubbed a “third nuclear age.” The first age was dominated by the Cold War between the United States and Soviet Union, the second by post–Cold War dynamics among various emerging and aspiring nuclear-weapons powers.

In a prescient 2019 essay, the scholars Nicholas L. Miller and Vipin Narang identified three main components of this new, third nuclear age: “renewed nuclear competition among several great powers” as arms-control agreements fall apart and these countries modernize their arsenals, the “emergence of new nuclear powers” (potentially including both U.S. allies and adversaries), and “a greater tolerance for escalation among existing nuclear powers.” North Korea’s work on tactical nuclear weapons testifies to the second and third dimensions.

This dangerous moment combines the challenges of great powers competing with and seeking to deter one another in the nuclear realm (the hallmark of the first nuclear age) with the challenges of stopping the proliferation of nuclear weapons (the focus of the second)—plus destabilizing new weapons systems and vanishing international cooperation to keep any of it in check.

The third nuclear age ushers the world into “truly uncharted waters,” the scholar David Cooper has observed. “Everything we think we know about nuclear weapons—deterrence, coercion, etc. … is based on a very short, finite history from two of the world’s most stable periods: the frozen, bipolar stalemate of the Cold War and then the subsequent … ‘unipolar moment’ of the post–Cold War world where the United States essentially was unrivaled in power.”

Tactical nuclear weapons are often described as “small” nuclear weapons, but that’s something of a contradiction in terms—like saying not to worry about the small asteroid barreling toward your town. The smallness holds only when compared with the kinds of “strategic” nuclear weapons that the U.S. and the Soviet Union threatened to obliterate each other with during the Cold War. Many tactical nuclear weapons in the American and Russian arsenals pack more potential explosive power than the U.S. atomic bomb that killed roughly 70,000 people in Hiroshima, although these explosive yields can be adjusted to lower levels.

After the Cold War, the U.S. scaled back its tactical nuclear weapons amid the triumphalism and diminished security threats of that period. But Russia largely maintained its stockpile, which is currently about nine times the size of America’s.

And as Ankit Panda of the Carnegie Endowment for International Peace has argued, if North Korea adopts tactical nuclear weapons, it would “manipulate [Schelling’s] slope” and “invite the United States and South Korea to stand on it.” North Korea is already predisposed to use its nuclear weapons early in a conflict with more powerful adversaries. The addition of tactical nukes, given their less destructive nature relative to strategic nukes, would further lower the bar for North Korean use of nuclear weapons. Deploying tactical nukes could involve Kim delegating some authority for command and control of those weapons to lower-ranking military commanders, particularly in wartime, and storing the weapons at more military bases throughout the country—which could significantly increase the risks of nuclear use as a result of accidents or miscalculations.

In, say, a non-nuclear conflict sparked by an act of North Korean aggression, Kim or one of his commanders, operating in the information-distortion field that is North Korea, could mistake a U.S. or South Korean retaliatory attack (or even something mundane, such as a civilian plane nearing North Korean airspace) for a more existential military offensive to wipe out the regime or its nuclear-weapons arsenal. They could respond by firing tactical nuclear weapons at U.S. or South Korean targets, leaving Washington and Seoul unsure about how to respond—particularly given U.S. qualms about again crossing the nuclear threshold and North Korea’s suspected capability to target the U.S. mainland with longer-range nuclear weapons.

North Korea could also deliberately turn to tactical nuclear weapons during an intensifying or stalemated conflict in an effort to spook its enemies and compel them to back down—an “escalate to de-escalate” strategy that the Russian military is thought to embrace.

The suddenly more real (if still very low-probability) prospect of Russian nuclear use in Ukraine is forcing policy makers, unpracticed in nuclear strategy and planning, to think hard about response options to such a brazen but bounded crossing of the nuclear threshold. In a similar vein, U.S. and allied officials need to proactively craft new policies and strategies for how to deter North Korea from using tactical nuclear weapons—and how to respond should deterrence fail. That could involve, for example, the U.S. and South Korean militaries making their bases less attractive targets for Pyongyang. It could also entail Washington and Seoul shifting their focus from the long-standing but now-quixotic goal of “denuclearizing” North Korea to engaging it in talks aimed at reaching arms-control agreements, reducing the threat that each side perceives from the other, managing crises before they spiral out of control, and mitigating the chances of a nuclear conflict erupting.

Former U.S. President Ronald Reagan and the former Soviet leader Mikhail Gorbachev famously declared that “a nuclear war cannot be won and must never be fought.” That reassuring sentiment was affirmed as recently as earlier this year by the five internationally recognized nuclear-weapons states. But in this third nuclear age, the line needs a corollary that recognizes the harsh realities of the times: Some nuclear-weapons states may indeed believe that a nuclear war can be won—and thus that one could be fought.

We often talk about the potential use of nuclear weapons in apocalyptic terms—as an act that would destroy the whole world. But that description of nuclear war as unthinkably horrific is a legacy of the Cold War. Limited use of nuclear weapons—use that could inflict tremendous destruction and shatter international norms but not destroy the world—is unfortunately thinkable. At the very least, it is incumbent upon policy makers to act as if it is thinkable; the very concept of tactical nuclear weapons is, in fact, premised on the idea that limited nuclear war is thinkable. We need to plan for such scenarios—even as we expend every effort to prevent them from materializing.