Great-power competition is back. With the post–Cold War unipolar moment over, the United States and China now jostle over trade and technology, compete in a conventional and nuclear arms race, and seek to counter the other in various hot spots. So far, China’s aggressive posture has yet to trigger a full-blown war, but the same cannot be said of Russia. Its invasion of Ukraine has confounded policymakers in the West and raised the specter of an increasingly dangerous, conflict-prone world.

What explains this turn for the worse? Political scientists tend to understand the behavior of challengers such as China and Russia in two ways. One camp views them as revisionist, expansionist, or “greedy” states: China and Russia want to revise the geopolitical status quo in pursuit of nationalist aims, great-power status, ideological dominance, or the ambitions of their authoritarian leaders. The second sees China and Russia as fundamentally insecure. To protect themselves against an external threat, insecure states may build up their military forces, seize territory that could form a buffer zone, or conquer a threatening adversary. In this view, competition is driven not by greed on the part of specific states but by the international system itself—and the insecurity it can create.

The debate is more than academic; each description leads to a very different policy. When a country faces a greedy state, the standard policy prescription is to deter it. In the case of China and Russia, then, the United States should strengthen its military advantages, communicate its resolve, and pursue economic and political policies to weaken these adversaries. When a country faces an insecure state, by contrast, the solution is not so simple. In that case, policymakers must reckon with a key concept in international relations theory: the security dilemma.

A security dilemma arises when an insecure state that seeks to protect itself acts in a way that unintentionally makes another state feel threatened and insecure. Tensions can escalate and lead to war, even though both sides merely want to live in peace. When it faces a security dilemma, the United States will be inclined to improve its deterrent capabilities. But it has to do so in a way that does not make its adversaries feel less secure, while convincing them that it desires only security. That can be a difficult needle to thread: after all, when a state builds stronger deterrent capabilities, an adversary can feel threatened. In grappling with the security dilemma, a state may be left with only bad options.

Finding the right option becomes even tougher when analysts think too rigidly about the nature of states, assuming countries belong to one of the two categories: either greedy expansionists or security seekers. Policymakers must aim to deter the former while waltzing through the security dilemma with the latter. But that binary distinction overlooks the fact that many states are mixed; they can be greedy and insecure at the same time and, therefore, especially hard to manage. Indeed, that is likely the case with the United States’ principal rivals today.

CRUEL INTENTIONS

The security dilemma has long been a fixture of international relations theory. The term was coined in 1950 by John Herz, who argued that states pursuing security in an anarchic international system “are driven to acquire more and more power in order to escape the impact of the power of others.” He went on: “This, in turn, renders the others more insecure and compels them to prepare for the worst.” Anarchy in international relations does not refer to chaos but instead describes the lack of an authority that can protect states from one another and enforce international agreements.

In the 1970s, Robert Jervis advanced the field’s understanding of the security dilemma by explaining that it became more or less acute depending on the relative might of offensive and defensive military capabilities, what scholars termed the “offense-defense balance.” In a 1978 essay, he explored the implications of changes in this balance. When states can build offensive forces more easily than they can build the requisite defenses to stave off attack, they will all seek to bolster their offensive capacities. As a result, they will feel more insecure, and competition will invariably intensify. By contrast, when defensive capabilities have the edge, states tend to be more secure and compete less.

Misjudging this balance can lead to catastrophe. In 1984, Stephen Van Evera argued that World War I resulted from the mistaken belief in the strength of offensive forces over defensive ones. Many European governments assumed that conquests would be easy, a belief that encouraged them to go to war. That conviction came apart in the bloody years that followed, as machine-gun and trench warfare made mincemeat of visions of easy conquest.

Studying the security dilemma helped scholars in the following decades transform realist understandings of international relations that saw competition and conflict as inevitable. Theorists such as Kenneth Waltz argued that in an anarchic world, states tend not to cooperate because they fear that others will take advantage of them—by cheating on agreements, for example. But in “Realists as Optimists,” an essay published in 1995, I showed how melding Waltz’s view of the international system with insights from studies of the security dilemma might point the way toward escaping the insecurity that the system generated. Cooperation and unilateral restraint, rather than competition and aggression, could in fact be the best options for a state in an insecure world. Take the Anti-Ballistic Missile Treaty, signed by the United States and the Soviet Union in 1972. The treaty essentially banned missile defense systems that would have threatened the adversary’s ability to retaliate for a nuclear strike—in other words, its capacity for deterrence. The treaty aimed to spare the superpowers an intensifying nuclear arms race that could have strained their relations and encouraged either of them to attack in a moment of crisis. Under the theory that scholars called “defensive realism,” states can be very secure when the security dilemma is mild—that is, when they find defense easier than offense and when a defensive strategy does not simultaneously provide a state with a more potent capacity to attack.

Other research of mine and by Andrew Kydd explored how competition driven by the security dilemma could lead states to see their adversaries as motivated by greed when they actually sought only security. A country could, for example, build up its army to provide itself with an extra margin of protection. But a rival might perceive that move as excessive and a sign of greed. The United States’ so-called pivot to Asia generated this type of dynamic. With China’s conventional military capabilities growing, the United States under President Barack Obama decided to give greater priority to East Asia, including by shifting more U.S. forces to the region. China believed that U.S. capabilities in the region were already extensive and sufficient for their stated purposes, however, so it perceived the change in U.S. policy as an act of hostility and aggression.

Scholars have explored the security dilemma’s reach in other arenas. Glenn Snyder explained that security-dilemma logic applies to alliance formation, as well as to military buildups. Much like the development of weapons that are good for both offense and defense, a new alliance can unsettle a rival, making that adversary wonder whether the pact is defensive or a precursor to future aggression. Barry Posen extended the security dilemma to ethnic conflicts that can erupt when imperial orders dissolve. In new conditions of anarchy, groups can see other groups as threatening even as each only seeks to defend itself. William Wohlforth applied the logic of the security dilemma to competition for status. A state’s anxiety about whether a peer recognizes its status can generate unnecessary competition. Scholars today apply this model even more widely—using it, for example, to examine how a conventional war might spiral into nuclear war.

As studies of the security dilemma demonstrate, governments have to worry about implementing policies that make other states feel less safe, because the heightened insecurity of others can be dangerous. During the second half of the Cold War, the United States and the Soviet Union chose to deploy multiple independently targetable reentry vehicles, or MIRVs, missiles loaded with several nuclear warheads. Both countries were ostensibly searching for greater security. But as a result of the deployment, the U.S. land-based ballistic missile force became more vulnerable and the United States worried intensely about the adequacy of its strategic nuclear forces. The arms competition also strained the superpowers’ diplomatic relationship, which made the new vulnerability of their nuclear forces seem all the more perilous. Both Washington and Moscow would have been more secure if neither country had deployed MIRVs.

The thorny dynamics of the security dilemma offer governments a variety of policy insights. Recognizing how its actions might make an adversary feel less safe, a state should lean toward defensive strategies, unilateral restraint, and negotiated agreements that limit the size and offensive attributes of its forces. Such policies can moderate the negative signals that military buildups can send to adversaries. An arms control agreement in the 1970s to ban MIRVs would have made the United States safer and eased Cold War tensions. States can sometimes become more secure by doing less.

BEYOND THE BINARY

Analysts have used the security dilemma framework to look at relations between states that seek security in an anarchic system. By contrast, they have recommended deterrence as the best policy option for dealing with expansionist states that are driven by greed. This binary framing neglects the fact that some states are mixed, both insecure and greedy.

These mixed states will never be satisfied with the status quo. Even if they are certain that their adversary merely seeks security, they will still be prone to behaving aggressively. Yet they are also likely to act aggressively if they feel insecure. Russia today may be a prime example of a country with mixed motives: it pursues aggressive policies in Ukraine both because it believes Ukraine should be part of Russia and because it feels threatened by NATO expansion.

Dealing with such an adversary is doubly difficult. A state would need to maintain a strong deterrent to ward off its adversary’s expansionist impulses. But maintaining a stronger deterrent makes it harder to forgo policies that decrease the adversary’s security, which could be self-defeating: feeling threatened, the adversary could become harder to deter. The difficult tradeoff created by the security dilemma would then intensify. Simply exercising restraint—with the hope of demonstrating one’s own peaceful motives—would likely be too risky. Any sign of weakness would tempt the adversary, now less deterred, to take aggressive actions.

The mixed motives of states increase the chances of confusion and misperception, greatly exacerbating the effects of the security dilemma. If a state fails to appreciate that its adversary faces such a dilemma, it will reach unduly negative conclusions. All threatening actions will be interpreted incorrectly as reflecting greedy motives—and confrontation and conflict will become more likely.

STARVED FOR CHOICE

The security dilemma can help analysts understand the Russian invasion of Ukraine and the military competition in East Asia between China and the United States. Neither case, however, reflects a pure security dilemma. And some interpretations depend on contested assessments of events on the ground.

At the risk of oversimplification, the debate over the causes of Russia’s invasion of Ukraine can be divided between those who emphasize the Kremlin’s greed and those who dwell on its sense of insecurity. The first perspective holds that the sources of the war are internal to Russia, including Putin’s particular beliefs about Ukraine’s history and a strain of imperial nationalism that has infected much of the Russian public. For analysts in this camp, Russia’s claims that it is threatened by the expansion of NATO are clearly disingenuous. This assessment of Russia—that it is greedy and secure—suggests that the best option for dealing with the Kremlin is deterrence and competitive policies; the United States should push for the expansion of NATO and strengthen its ability to attack or coerce Russia.

The other perspective holds that NATO’s eastward expansion—along with the promise officials made in 2008 that Ukraine would eventually become a member and the growing political and military relationship between the treaty organization and Ukraine since then—created genuine Russian insecurity. To prevent NATO from encroaching farther into the former Soviet Union, the argument runs, Russia invaded Ukraine. These analysts see the security dilemma in action, with NATO’s search for security making Moscow feel threatened and insecure. Alternatively, it could be argued that NATO was a greedy actor with expansionist goals that had nothing to do with its own security: it wanted to spread democracy, expand the liberal international order, and enlarge the reach of the West. In this view, the alliance did not face a security dilemma but instead adopted greedy policies that made Russia insecure and provoked it to invade.

This polarized debate largely overlooks the possibility that instead of being either greedy or insecure, Russia is both. In this reading, Russia had designs on Ukraine well before NATO moved toward including Ukraine in the alliance. Then, NATO’s looming expansion made Russia feel insecure, which in turn made the Kremlin more likely to act in expansionist ways. An invasion of Ukraine became Russia’s best option.

If Russia is indeed a mixed state, then the West probably never had good options to prevent the invasion. Giving up on NATO expansion might have delayed it but would not have stopped it. As Russia became more powerful, the Kremlin might have invaded just to satisfy its greedy motives no matter what NATO did. And because Ukraine was not in the alliance, NATO could not pursue a purely defensive strategy in deterring a Russian attack. Had NATO been more aggressive and decided to accept Ukraine as a member, it would have unavoidably decreased Russian security. But the slow process of the alliance’s expansion—raising the possibility of Ukraine’s inclusion but still excluding it—appears to have been the worst of both worlds. It may have made Russia feel insecure without sufficiently deterring a Russian invasion.

The security dilemma also looms large over the rivalry between the United States and China. In some respects, there should be little cause for military tension. The vastness of the Pacific Ocean makes invasion of each other’s homeland virtually impossible. That both countries are large and of roughly equal power also makes invasion less likely. In addition, both can deploy nuclear forces that can endure nuclear strikes, providing highly effective deterrents. Distance, the ocean, and nuclear weapons strongly favor defense. As a result, the security dilemma here is so mild that China and the United States should have little difficulty avoiding security competition.

But zoom in on East Asia, and the dynamic changes entirely. The security dilemma in this region and specifically over Taiwan is complex and dangerous. China considers Taiwan part of its homeland and wants to achieve unification with the island. It sees its efforts to prevent Taiwan from declaring formal independence as geared toward preserving its own territorial integrity and thus its national security. Chinese officials consider the possibility of using force to achieve unification a matter of security, not greedy expansion.

The United States does not take an official position on the outcome of Taiwan’s status, but it rejects the use of force as a legitimate means for resolving the dispute and is committed to maintaining the United States’ ability to defend the island. The situation is therefore not, strictly speaking, a security dilemma but a dispute over the political status quo and the acceptable means for that dispute’s resolution.

The dynamics of a security dilemma nevertheless intensify the competition over Taiwan. Even purely defensive capabilities deployed by Taiwan and the United States would appear threatening to China because they could increase Taiwan’s willingness to declare independence and reduce China’s ability to coerce or invade the island. Consequently, even if the conditions that would usually blunt a security dilemma were available—such as highly effective defense capabilities that do not double as offensive capacities—they would do little to reduce competition and China’s insecurity. Instead, China would see the United States as a threat and respond in ways that then threaten Taiwan. As China’s power and military potential increase, so will military competition and political tensions.

The United States is therefore left with only bad options. It can toughen Taiwanese defenses and its own commitment to safeguarding the island but will thereby continue to threaten China’s security and risk a major war. It can implement that policy in a variety of ways, but not in one that solves the fundamental problem: that China sees Taiwan as a vital interest. Alternatively, the United States can end its commitment to using force to defend Taiwan, potentially inviting a Chinese invasion and the forcible unification of the island with the mainland. There are no options in between.

Although it is not applicable in every situation, the security dilemma helps explain much of great-power competition. But as these cases show, even the strongest theory cannot be easily applied in all situations. Categorizing states as greedy or insecure may help conceptual models function, but it flattens the drivers of state behavior in the real world. As ever, some of the hardest problems for policymakers and analysts lie in the gray areas that resist easy solutions.