Which is more dangerous: The revisionist power on the ascent or the revisionist power in decline? We naturally tend to think it is the former. “It was the rise of Athens and the fear that this inspired in Sparta that made war inevitable,” Thucydides famously wrote.¹ That line is often interpreted as meaning that rising revisionists—states dissatisfied with the current international system—display growing ambition, assertiveness, and impatience. This behavior elicits a hostile response by the reigning hegemon; tensions spiral and war results. This view of how great-power wars begin—call it the Thucydidean formula—shapes our understanding of global affairs even today.

Certainly, rising revisionists can create profound geopolitical friction: Note how China and Russia have used their resurgent power to disrupt the U.S.-led international system, and the increasing alarm that behavior has stirred among the Washington policy elite and American allies. Yet we often lose sight of a different pathway to great-power war, for peril may emerge when a country that has been rising, eagerly anticipating its moment in the sun, peaks and begins to decline before its ambitions have been fulfilled. The sense that a revisionist power’s geopolitical window of opportunity is closing, that its leaders cannot readily deliver the glories they have promised the population, can trigger rashness and risk-taking that a country more confident in its long-term trajectory would avoid.

Indeed, this combination—ambitions fired by a revisionist power’s ascent, followed by the fears that emerge when a premature fall begins—has historically created some of the most dangerous moments in great-power relations. It is also a combination worth worrying about today. American strategists are properly concerned about how Russia and China will behave if they become more capable of contesting U.S. leadership; dealing with a rising China in particular may be one of the greatest challenges American statecraft has ever confronted. Yet they should be no less concerned about how those countries will act as their relative power starts to fade.

The dangers created by a rising revisionist power are obvious. As a dissatisfied nation accrues greater strength, the state uses that strength to avenge perceived slights and attain greater influence. It enlarges its definition of national interests; and it defends those interests more vigorously. Constraints and threats that seemed tolerable when the state was weaker come to seem intolerable as it gains the power to affect them. And as the rising state behaves more assertively, its ambitions inevitably collide with the interests of established powers and their allies. Progressively sharper moves and counter-moves typically ensue; competition intensifies; the system plunges into military conflict.

This sequence sounds familiar because it has played out many times. World War I was a lot of things, but it was partially a clash between Germany, which was seeking to translate its growing economic and military might into a position of European dominance and global power, and the United Kingdom, which was determined to protect its European interests and global primacy. During the Cold War, too, arguably the most dangerous moments came when the growth of Soviet military capabilities tempted the Kremlin to more boldly assert its interests against the West.

Shortly after Stalin acquired nuclear weapons, he authorized the North Korean invasion of South Korea, causing global tensions to rise. When the Soviets subsequently acquired a ballistic missile capability, Nikita Khrushchev used this power to pursue gambits—trying to foreclose Western access to Berlin, deploying nuclear missiles to Cuba—that brought the world to the brink of war. Fear of being overtaken by the Soviets, in turn, sometimes pushed American leaders to consider risky policies of their own. In the late 1940s and early 1950s, some American strategists—and some wayward philosophers like Bertrand Russell—advocated waging preventive war before the Kremlin acquired usable nuclear weapons, for fear it would be impossible to contain Moscow once that threshold had been crossed.²

Fortunately, the Thucydidean formula never reached its grim conclusion during the Cold War. But the underlying pressures were there, and they have reappeared as great-power competition has surged anew.

As Russia recovered from its post-Cold War weakness beginning in the early 2000s, it made progressively stronger moves to reclaim lost influence and prestige. By waging wars of conquest against vulnerable, Western-oriented neighbors such as Georgia and Ukraine, by projecting military power and geopolitical influence into the Middle East, by interfering in U.S. elections and using a variety of measures to sap the strength and cohesion of the nations opposing it, Russia has shown that it no longer accepts the unipolar order that prevailed after the Cold War.

And as Chinese power has grown exponentially over the past quarter-century, Beijing has become steadily more assertive in challenging American influence in the Asia-Pacific and globally. Beijing’s creeping expansionism in the South China Sea and East China Sea, its efforts to draw the countries along its periphery and beyond into its economic and geopolitical orbit, and its development of more advanced military capabilities and projection of both military and economic power ever farther abroad have produced growing fears among Washington and its allies. Observers such as Harvard’s Graham Allison have warned, not implausibly, that Washington and Beijing may be headed for a great hegemonic war like the one between Athens and Sparta.³

There is, then, no disputing that rising powers can have profoundly disruptive effects. Yet such powers might not actually be the most aggressive or risk-prone type of revisionist state. After all, if a country’s position is steadily improving over time, why risk messing it all up through reckless policies that precipitate a premature showdown? Why not lay low until the geopolitical balance has become still more favorable? Why not wait until one has surpassed the reigning hegemon altogether and other countries defer to one’s wishes without a shot being fired? So while a rising revisionist power may be tempted to assert itself, it should also have good reason to avoid going for broke.

Now imagine an alternative scenario. A revisionist power—perhaps an authoritarian power—has been gaining influence and ratcheting its ambitions upward. Its leaders have cultivated intense nationalism as a pillar of their domestic legitimacy; they have promised the populace that past insults will be avenged and sacrifices will be rewarded with geopolitical greatness and global prestige. Yet then the country’s potential peaks, either because it has reached its natural limit or because of some unforeseen development, and the balance of power starts to shift in unfavorable ways. It becomes clear to the country’s leadership that it may not be able to accomplish the goals it has set and fulfill the promises it has made, and that the situation will only further worsen with time. A roll of the iron dice now seems more attractive: It may be the only chance the nation has to claim geopolitical spoils before it is too late. In this scenario, it is not rising power that makes the revisionist state so dangerous, but the temptation to act before decline sets in. In this sense, the dynamic bears a resemblance to the famous Davies J-Curve theory of revolution, wherein a populace is held to be more inclined to revolt not when it is maximally oppressed but rather when raised expectations are shown to be in vain.

Obviously, rational analysis does not always prevail in world politics. Rising states can become intoxicated with their own strength; they may simply get tired of waiting to attain the status they desire; or some domestic pressure may impel leaders to act dangerously. But revisionists whose power has begun to decline, or who have hit a rogue bump in the road, may not feel that they even have the option of waiting.

Consider again the outbreak of World War I. From a long-term perspective, Germany may have been a rising and increasingly confident power prior to the war, but Berlin’s decision-making in 1914 took place against the more immediate backdrop of deep pessimism caused by the fear of impending decline. In the east, Germany was menaced by the growth of Russian military power and the approaching completion of an improved railroad network that would dramatically shorten Russia’s mobilization timetable. In the west, changes in French conscription laws were rapidly enhancing the military manpower of another rival.

The result, in Berlin, was mounting apprehension that Germany’s ability to fight a two-front war—the cornerstone of its military strategy—was about to collapse, and that its geopolitical aspirations were about to be crushed in a Franco-Russian-British vise. If that happened, internal frictions might become unmanageable: Nationalism and geopolitical ambition might no longer be able to dampen the shocks caused by intensifying conflicts between rival social and political groups. This is why Germany ran such enormous risks in the July 1914 crisis—by pushing Austria-Hungary to take an uncompromising position against Serbia after the assassination of Archduke Franz Ferdinand, by promising to back the Dual Monarchy come what may, by implementing the Schlieffen Plan for a knock-out blow against France despite the danger that this would bring Britain into the war. Chief of General Staff Helmuth von Moltke acknowledged the danger of a “war which will annihilate the civilization of almost the whole of Europe for decades to come,” but he and his colleagues pushed forward on grounds that Germany’s dreams of greatness would become hopeless illusions if not realized soon.⁴

Similar motives were at work in World War II. Hitler’s Germany had the most radical designs of any revisionist power in history, and it is inconceivable that Hitler would not have used Germany’s revived economic and military might to precipitate a major conflict at some point. Yet Hitler’s calculations about when and how to do so—namely, by invading Poland in 1939—were strongly influenced by fears of imminent decline.

Due to rapid rearmament, the Germany economy was overheating by 1938-39, creating concerns that Berlin’s relative economic power would soon fade absent additional conquests. Just as importantly, German officials believed that their early rearmament and the absorption of resources from Austria and Czechoslovakia had given them a critical military advantage over other European powers, but that this advantage would fade as those countries—and the United States—began mobilizing. It had become necessary “to begin immediately,” Hitler explained to Mussolini to following year, “even at the risk of thereby precipitating the war intended by the Western powers.”⁵ In the same vein, the sense that the future would only be worse—that Germany had reached the apex of its power, that it must act boldly while it still could—underpinned the decision to invade the Soviet Union in June 1941. As Timothy Snyder has argued, Hitler believed that Germany had only a finite window to seize and colonize Soviet lands—thereby solving the Third Reich’s food supply problems and making it strategically invulnerable—before ongoing British resistance and America’s feared entry into the war began to undermine Berlin’s position.⁶

Japan, too, was likely influenced by calculations of impending decline. The Japanese empire had been steadily expanding between 1931 and 1940, advancing toward dominance in the Asia-Pacific. But what ultimately provoked the Japanese to strike at America was the realization that the possibilities for attaining that dominance were fading. American rearmament, symbolized by the Two-Ocean Navy Act of 1940, was bound to vitiate Japanese military advantages. “Anyone who has seen the auto factories in Detroit and the oil fields in Texas knows that Japan lacks the national power for a naval race with America,” warned Admiral Yamamoto Isoroku.⁷ Likewise, the U.S. oil embargo of 1941 had the unintended effect of convincing Japanese leaders that they had to move quickly before they lost the economic wherewithal to wage war. Imperial Japan, like Nazi Germany, was an aggressive power with enormous ambitions; but its penchant for aggression grew strongest when it started to fear those aspirations might not be realized.

This history has implications for understanding great-power rivalry today. Both Russia and China have broadened their geopolitical horizons in recent years; both are often thought of as rising or resurgent powers. Yet both Russia and China face the prospect—whether immediate or more distant—that their relative strength may ebb, a phenomenon that could make these countries more aggressive rather than less.

The specter of decline surely haunts Vladimir Putin. Russia has compiled an impressive record of expansion over the past decade; it has achieved a significant military overmatch vis-à-vis NATO on the alliance’s eastern flank; it has attained a degree of global influence greater than that enjoyed by any government in Moscow since the 1980s. Yet Putin cannot be confident about Russia’s long-term trajectory.

After all, Russia’s economic revival from the early 2000s onward was largely a function of high energy prices; the collapse of those prices after 2014 revealed the long-term weakness of an economy that is probably destined—absent another sustained period of high energy prices—to stagnate over time. Russia is already losing ground against its rivals: Its inflation-adjusted GDP declined from 2014 through 2017, while that of the United States increased by over $1 trillion.⁸ And although Russia’s demographic trajectory is no longer as catastrophic as it once was, population growth will be anemic at best and negative at worst in coming decades. These trends, combined with the impact of Western economic sanctions, are beginning to upset Putin’s plans for continued military modernization: Kremlin defense spending declined, perhaps by as much as 20 percent, from 2017 to 2018, as Russia also began to cut spending on key social programs and pensions. Finally, fear of political instability is omnipresent for Russian leaders, who must deal with separatist forces in the North Caucasus as well as dissent provoked by their own repression and policy incompetence.

Putin surely understands that these challenges imperil his goals of reasserting Russian dominance within the near abroad and playing a pivotal role in a more multipolar world—which is precisely what makes his statecraft so dangerous. Putin has already established a reputation as a risk-taker who uses bold strokes to compensate for Russia’s limited resource base. His method is to know what he wants and to catch stronger adversaries napping. (That tendency has only become more pronounced in recent years as Russia’s economic prosperity has faded and Putin’s domestic popularity has begun to wane.) He has argued that Russia requires authoritarian rule to be influential abroad; he has promised the Russian populace that the hardships it has endured will be rewarded by greater global stature. “Enormous sacrifices and privations on the part of our people,” he has declared, are the cost of “occupying a major place in world affairs.”⁹ If Putin perceives that he has only limited time to deliver on these promises, if he senses that the opportunity to redress his longstanding grievances against the West is slipping away, the effect may be to encourage still greater risk-taking.

Russian risk-taking could take varied forms: more aggressive behavior in a crisis with NATO in the Baltic or Black Sea regions, perhaps aimed at discrediting NATO’s Article 5 guarantee; a more confrontational posture with respect to America and its partners in Syria or another Middle Eastern hotspot; intensified Russian efforts to disrupt U.S. and European electoral processes; more damaging cyberattacks on critical Western infrastructure; efforts to stir up additional “frozen conflicts” in the former Soviet space; a stronger propensity for escalation—perhaps involving limited use of nuclear weapons—should conflict between Moscow and Washington break out. Whatever the specifics, Washington could find itself facing a competitor with a “now-or-never” mentality—always a dangerous mindset for an authoritarian, revisionist state to have.

By contrast, the Chinese leadership still seems to have a “time is on our side” mindset. Even as Beijing’s energy and assertiveness have surged, Chinese leaders have proven less risk-acceptant than their Russian counterparts. They have remained satisfied to advance China’s aims through small, incremental steps—such as island-building and coercion in the South China Sea—rather than dramatic, aggressive lunges. Yet even Chinese leaders cannot be confident that the country’s upward trajectory will continue unbroken for very much longer.

In a geopolitical sense, Chinese officials must worry about whether the country’s window is opening or closing with respect to issues like Taiwan. For while China has greater military capability than ever before to pursue reunification through forcible means, Taiwanese support for peaceful unification is at rock-bottom levels, the development of a distinctive Taiwanese national identify becomes more unmistakable every year, and the political pendulum in Taipei is clearly swinging away toward greater resistance to Chinese pressure.

There are also warning lights flashing—perhaps flashing in the distance, but flashing nonetheless—when it comes to the fundamentals of Chinese power. Economic growth has been broadly declining for at least a decade (although it may have ticked upward slightly last year), according to official government estimates that are almost certainly inflated. China suffers from astronomic debt levels and has seen dizzying volatility in its stock market, both of which may be precursors to bigger economic troubles ahead. The demographic problems China confronts are even more severe than Russia’s: The rapid aging of the population will strain social spending, inhibit growth, and confront Chinese leaders with sharper guns-versus-butter trade-offs.

Beneath the façade of stability imposed by increasingly repressive governance, moreover, dissatisfaction with a corrupt and autocratic elite is increasing: Chinese officials stopped publicly reporting the number of “mass incidents” in 2005, but the frequency of such incidents is widely believed to be rising. If the drastic domestic security measures taken in areas such as Xinjiang and Tibet are any indication, major sections of the country seem to be seething with discontent. Add in the fact that China’s behavior is stirring greater fears not just in Washington but throughout the Asia-Pacific and beyond, and Beijing may soon find itself dealing with greater geopolitical pushback, including the development of military capabilities designed specifically to neutralize the leverage provided by China’s own build-up. As unlikely as it may seem right now, it is entirely possible that sometime in the next decade or two, Chinese leaders may have to face a future that is not so bright and shining as seems the case now.

When this happens, will Beijing become more or less aggressive on the global stage? The answer may well be “more.” Xi Jinping and other Chinese leaders have been promising that the nation is on the verge of achieving national rejuvenation, that it can now take center stage in world affairs. The regime has assiduously stoked Chinese nationalism; it has staked out inflexible positions on maritime disputes and other issues; it has even begun to issue soft deadlines for reunification with Taiwan. It has done so on the assumption that the continued growth of national power will enable Beijing to make good on its pledges and back up its demands.

If that assumption does not hold, if the “Chinese Dream” begins to elude its dreamers, Chinese leaders may be tempted to take more dramatic steps rather than admitting that they cannot deliver. In these circumstances, an attempt to retake Taiwan by force or coercion, to teach Japan a lesson in the East China Sea, to break Vietnamese or Filipino resistance in the South China Sea, or to rupture America’s alliance system in the Asia-Pacific would still be highly dangerous. But these initiatives might come to seem more attractive than simply remaining passive while Beijing’s relative power fades.

Robert Kaplan has put it aptly: If a confident China has been pursuing a “methodical, well-developed” strategy of revisionism, an insecure China could shift to “daring, reactive, and impulsive behavior.”¹⁰ Limiting the damage done to U.S. interests by a rising China will be a test of epic dimensions for American policymakers. But the moment of peak danger in the relationship may actually come when China starts to fade from its own wishful trajectory.

All this poses a genuine dilemma for U.S. policymakers, who must contain the ambitions of today’s revisionist powers without encouraging desperate behavior that might lead to war. One way of addressing this dilemma would be simply to take steps that ease American rivals’ perceptions of insecurity and decline—by conceding them larger spheres of influence that might satisfy their ambitions, or by declining to build military capabilities or strengthen alliances that might undercut those rivals’ positions and thereby exacerbate their fears. Yet the downside of this approach is obvious: It would require Washington to sacrifice some key interests and forego some of the strengths needed to sustain them. The United States might decrease the danger that a declining challenger would behave rashly, but only by exposing itself to other perils.

What will be required instead is a combination of careful prudence with great strength and resolve. U.S. leaders must not gratuitously antagonize U.S. rivals or put them in situations where they fear they must use their power before they lose it. This means staying away from efforts to overthrow or seriously destabilize the Russian and Chinese regimes (although perhaps not from more measured efforts to raise the costs of authoritarianism within those countries). It means avoiding acts, such as supporting a Taiwanese declaration of independence or excluding Russia from the SWIFT payments system—that would foster a “little to lose” mentality in Moscow or Beijing. Additionally, when Washington must issue explicit warnings—about Beijing’s behavior in the South China Sea, or about Russia’s meddling in U.S. political processes—it should do so privately, to minimize the reputational cost that American competitors must pay by backing down. As Dwight Eisenhower said during another great-power competition, America should carefully consider “how much we should poke at the animal through the bars of the cage.”¹¹ Such caution is especially important when the animal is already frightened.

Yet the counterpart to prudence must be unmistakable military strength and geopolitical resolve. The challenge in dealing with declining revisionists is that their calculations of risk and reward may shift suddenly, and in potentially explosive ways: Actions that seemed unattractive or unthinkable before become more appealing as the perceived costs of inaction rise. The imperative, therefore, is to manifest a level of power and commitment sufficient that even a more risk-acceptant rival will understand that a geopolitical gamble is highly unlikely to pay off. This requires restoring the military supremacy necessary to defeat Russian or Chinese gambits in the Baltic, the Western Pacific, and elsewhere, and cultivating—across the entire array of U.S. foreign policy decisions—a reputation for credibility in upholding American commitments against revisionist challenges. The better the record the United States compiles in standing up to Chinese and Russian probing behavior in the near-term, the less likely the leadership of those states will be to think that more dramatic action will succeed at some point down the road.

A balance of firmness and caution is always difficult to strike, but it is never impossible. After all, there have been instances in which America has successfully managed the eclipse of a dangerous revisionist power. The Soviet Union might have tried to escape the dilemmas of terminal decline in the 1980s by pursuing a more aggressive policy, but it didn’t. It opted not to do so in part because the Reagan and Bush Administrations offered assurances that they were not seeking the destruction of the Soviet state (which happened anyway, mostly for other reasons) and that they would not publicly humiliate Soviet leaders. Yet the Soviets also chose restraint because America and its allies had amassed, throughout the Cold War and during the 1980s in particular, sufficient power and credibility such that more aggressive Kremlin policies would not be rewarded.

Given the degree of disruption China and Russia are posing today, managing the decline of ambitious revisionist powers is the sort of problem American strategists might love to have. Yet doing so effectively will be a major geopolitical challenge in its own right, if things roll that way. It will demand, once again, a mixture of flexibility and strength.