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date: 19 August 2018

Population Aging and International Conflict

Summary and Keywords

Most of the world has experienced a revolutionary and unprecedented development over the course of the last century and especially since the end of the Second World War: significant population aging. By any standard measure—median age, the number of 60- or 65-year-olds and over as a percentage of a population, or old-age dependency ratios (the ratio of seniors to working-age adults), most of the world is significantly older today than in the middle of the 20th century, and the trend is accelerating.

The world’s great powers have not been immune to this trend. To the contrary, many of these countries have been leading the way, aging faster and to a greater extent than most other countries. By 2050, the median age of China, France, Germany, Japan, Russia, the United Kingdom, and the United States will be at least 40. Germany and Japan are currently two of the oldest countries in the world, and China is likely aging faster than any other country in history.

How is the near worldwide phenomenon of population aging likely to affect international relations (IR)? Most scholars who have examined this issue have linked the potential effects created by aging to established IR theories. Most analyses that have developed around the issue of aging, in other words, have not created new theoretical approaches to the study of international politics. They have instead argued that aging is likely to affect key variables associated with existing IR theories, which will then tend to generate particular outcomes based on these theories’ predictions. The IR theories that studies of populating aging have most frequently tied into include ones from realist, diversionary war, and constructivist research programs. Many of the arguments that link the effects of aging to these theories reach opposite conclusions, with some predicting a much higher probability of international conflict due to aging, others the reverse. There are, however, very few empirical analyses that test these competing hypotheses, largely because aging is such a new phenomenon.

Keywords: population aging, demography, international conflict, empirical international relations theory, power transition theory, window theory, ideology, ideological polarization, diversionary war theory, geriatric peace, constructivism


Most of the world has experienced a revolutionary and unprecedented development over the course of the last century and especially since the end of the Second World War: significant population aging. By any standard measure—median age, the number of 60- or 65-year-olds and over as a percentage of a population, or old-age dependency ratios (the ratio of seniors to working-age adults), most of the world is significantly older today than in the middle of the 20th century, and the trend is accelerating.

The world’s great powers have not been immune to this trend. To the contrary, many of these countries have been leading the way, aging faster and to a greater extent than most other countries. By 2050, the median age of China, France, Germany, Japan, Russia, the United Kingdom, and the United States will be at least 40.1 Germany and Japan are currently two of the oldest countries in the world, and China is likely aging faster than any other country in history.

How is the near worldwide phenomenon of population aging likely to affect international relations (IR)? Most scholars who have examined this issue have linked the potential effects created by aging to established IR theories. Most analyses that have developed around the issue of aging, in other words, have not created new theoretical approaches to the study of international politics. They have instead argued that aging is likely to affect key variables associated with existing IR theories, which will then tend to generate particular outcomes based on these theories’ predictions. The IR theories that studies of populating aging have most frequently tied into include ones from realist, diversionary war, and constructivist research programs. This article summarizes the main arguments on the subject. Its analysis concentrates primarily on the great powers because these states possess the greatest capacity to shape international politics.

Many of the arguments that link the effects of aging to IR outcomes reach opposite conclusions, with some predicting a much higher probability of international conflict due to aging, others the reverse. There are, however, very few empirical analyses that test these competing hypotheses, largely because aging is such a new phenomenon.

Aging and Realist IR Theories

The set of IR theories that studies of aging most frequently utilize come from the realist tradition. This is not surprising. The most obvious and one of the most important ways in which aging is likely to shape states’ foreign policies is by affecting their military capabilities, which are the central focus of realist analyses.

Aging is likely to have three major effects on states’ capabilities (Haas, 2007, pp. 112–147; Haas, 2012, pp. 49–62). The first is by slowing economic growth. A state’s gross domestic product (GDP), in its most basic formulation, is a product of the number of workers and overall productivity. As a country’s workforce shrinks as more people enter retirement than enter the labor market, so, too, will its GDP unless productivity levels rise sufficiently to compensate for this loss. Between 2010 and 2050, Japan’s working-age population (ages 15 to 64) is expected to shrink by 32%, Russia’s by 23%, Germany’s by 22%, and China’s by 18%. To prevent these workforce reductions from translating into overall GDP decline, states’ productivity must increase proportionally. Although this is likely to be the case in most of the industrialized countries, workforce contraction will still act as a substantial brake on economic growth in coming decades.2

Compounding these problems, significant social aging may also limit productivity growth. The elderly are likely to be more conservative with their investments than younger people. The more risk averse a society’s investment portfolio, the less entrepreneurship that will be funded, and thus the lower the gains in productivity that should be expected. National savings rates may also shrink in aging states as large numbers of seniors spend down their savings. The savings rate in Japan, for example, was long one of the highest in the world. It is currently below zero as Japanese citizens spend more than they earn. Aging played a major role in causing this shift (Soble, 2015). Reduced savings rates may lead to rising interest rates, which are likely to impede economic growth by shrinking investment.

The effects of these dynamics created by aging on states’ military capabilities are obvious. The slower states’ economic growth, the less we should expect significant increases in military expenditures. Reductions in defense spending are instead more likely in periods of economic stagnation.

A second way in which population aging is likely to negatively affect states’ military power is through the creation of crowding out dynamics: The more that governments spend on elderly welfare, the less they are likely to spend on all other purchases, including on the military. All governments in the industrialized world have made commitments to pay for substantial portions of the retirement and health-care costs of their elderly citizens. The projected increases in governmental spending for the elderly in coming decades are massive. Annual public benefits to the elderly (both pension and health care) as a percentage of GDP are forecasted to rise between 2010 and 2040 by 7.6 percentage points in China (to an overall percentage of 11), by 7.4 percentage points in the United States (to an overall percentage of 18.5), by 7.3 percentage points in Germany (to an overall percentage of 24.3), by 5.8 percentage points in Japan (to an overall percentage of 20.9), by 5.7 percentage points in France (to an overall percentage of 24.3), by 5 percentage points in the United Kingdom (to an overall percentage of 18.9), and by 2.7 percentage points in Russia (to an overall percentage of 10.9) (Jackson, Howe, & Peter, 2013, p. 14). These expenditures on the elderly will create a very tight fiscal environment that will put pressure on all other areas of spending.

Finally, aging is likely to affect states’ capabilities by pushing militaries to spend more on personnel and less on other areas, including weapons development and procurement. Aging, in other words, will tend to affect not only the size of military budgets, but its composition. Aging societies are likely to dedicate a growing percentage of their military budgets to personnel expenditures for two main reasons. First, as societies age, more people exit the workforce than enter it. Increasing numbers of retirees in relation to new workers are likely to create labor shortages relative to previous levels of employment. The result of this trend will be increased competition among businesses and organizations—including the military—to hire workers. Consequently, if states’ militaries want to be able to attract and keep the best employees, they are going to have to pay more to do so.

A second factor that is increasing states’ military personnel costs at the expense of weapons procurement is the aging of the military itself. The great powers’ pension obligations to retired military personnel are considerable. Russia, for example, in the 2000s consistently spent significantly more on military retirees than on either weapons procurement or military research and development (Haas, 2007, p. 142). Similarly, rising pension costs, according to China’s government, were the second most important reason (after pay increases for active personnel) for increases in Chinese military spending in the 1990s and 2000s (People’s Republic of China, 2004).

Given these relationships, it is not surprising that the oldest of the great powers are already devoting significantly more resources to military personnel than weapons purchases and research. In 2016, Germany spent nearly 3.5 times as much on personnel expenditures than military equipment, France almost twice as much (NATO, 2016). Increasing personnel costs as a percent of Japan’s military budget, according to Brad Glosserman and David Kang (2014), have helped make claims of Japanese “remilitarization” due to increases in military spending in recent years a “myth.”

Growing military personnel expenditures due to increasing per-unit labor and pension costs will reduce states’ ability to project power. Unless military budgets are expanding (and aging’s negative effects on economic growth makes this less likely), increasing per-unit labor costs will result in a reduction in the number of military personnel. In these conditions, the same amount of money will pay for fewer soldiers. Growing pension costs for military retirees not only do not add to states’ capabilities, but likely subtract from them due to crowding out dynamics.

How is the probability of international conflict likely to be affected by the major negative effects that aging will tend to have on states’ military capabilities? Analysts have answered this question in very different ways, with some predicting an increased likelihood of international conflict and others the reverse, depending on which variety of realist theories they utilize. Scholars who predict that aging is likely to result in an enhanced likelihood of international conflict most frequently rely on two sets of arguments: power transition and “window” theories.

A power transition occurs when a state that is inferior to another in terms of relative power becomes superior. This transition augments the likelihood of conflict in two main ways. First, it creates incentives for preventive hostilities. If the declining state is convinced of the enmity of the rising state, the incentives to attack the latter before the power transition is complete are strong. Waging a preventive war against a rising enemy maximizes the probability of victory because the declining state will be fighting when its relative power advantages are at their greatest level. Second, a power transition increases the likelihood of conflict from the perspective of the rising state. Once the transition is complete, the newly-dominant country confronts incentives to use force in order to alter the territorial and institutional status quo in its favor to be more commensurate with the new power realities (Copeland, 2000; Kugler & Lemke, 2000).

The relationship between power transition theory and population aging is straightforward. The aging problem in a particular country may be so severe that it creates a power transition between this state and a potential rival, for which the challenges of aging are not as acute (Yoshihara, 2012, p. 141).

China’s relationship with India in coming decades may be a prominent example of this dynamic at the great power level (Chang, 2012, pp. 173–174; Curtis, 2012, pp. 190–197). The costs of aging may be instrumental in creating a power transition between a declining China and a rising India. Whereas China’s working-age population is forecasted to shrink by 18% between 2010 and 2050, India’s will increase by 45%, or over 350 million people (India’s working-age population in 2050 will be bigger than China’s by the same number). Because of its relatively youthful demographic profile, India’s obligations to the elderly will remain modest, both absolutely and relative to China’s. Whereas China’s public benefits to seniors are predicted to increase between 2010 and 2040 by 7.6% of GDP to an overall percentage of 11, India’s obligations are forecasted to rise by only 0.6% of GDP to an overall percentage of 2.5 (Jackson, Howe, & Peter, 2013, p. 14). India’s economy is currently growing faster than China’s, and the gap is likely to grow in coming decades due in part to India’s major demographic advantages (“Catching the Dragon,” 2015; Whalen, 2015). If China’s leaders anticipate a power transition with India, they will confront incentives to initiate preventive hostilities, especially given the history of rivalry and territorial disputes between the two countries. If the transition takes place and India becomes the stronger power, its leaders will confront incentives to take advantage of this superiority to advance their interests at China’s expense.

A second way in which declining military capabilities caused by populating aging can increase the likelihood of international conflict is based on the insights of “window” theory. If leaders anticipate a significant decline in their relative power, they may reason that they possess a shrinking window of opportunity to achieve any international objectives that are likely to require the use of force. This view will create incentives to aggress while power distributions are at their most advantageous (Lebow, 1984).

This logic has obvious similarities to that of Power Transition Theory. What makes closing windows of opportunity even more dangerous is that their activation is not dependent on the anticipation a full-blown power transition that occurs when one state becomes more powerful than another. A less powerful country may be pushed to take aggressive actions against the interests of a stronger one if its leaders’ feel their country’s relative power has peaked (Japan’s attack on Pearl Harbor in 1941 is a classic example of this dynamic), just as a stronger state may feel compelled to aggress against a weaker one even if it never fears losing overall power superiority. Even if leaders believe that their state will never become inferior to another, they would still want to wage any conflicts that are likely to occur when power distributions are most in their country’s favor. In either case, the anticipation of relative power plateauing will result in increasing pessimism about a country’s ability to achieve revisionist international goals in the future, which will increase the incentives for aggression in the present.

The costs created by population aging may very well cause fluctuations in power distributions that create closing window-of-opportunity dynamics. Even more troubling, leaders of countries with aging populations may be particularly inclined to act on these incentives. Two factors, operating in tandem, lead to this conclusion. First, individuals, including political leaders, tend to be particularly willing to take high levels of risk, including the threat or use of force, when they experience or anticipate losses. This is the central finding of the psychology-based “Prospect Theory” (Haas, 2001). Second, aging is likely to place people in loss frames, both by creating costs that negatively affect power distributions and by creating doubts about the long-run viability of a nation. As Susan Yoshihara expresses the latter relationship: “There appears to be a very clear correlation between population decline and rising strategic pessimism. Eroding demographic prospects have changed the national mood [for the worse] in Japan, China, and throughout Europe” (Yoshihara, 2012, p. 216). These trends may make an aging world a dangerous one if leaders become willing to be particularly aggressive to prevent or recoup losses.

Scholars have hypothesized that the costs created by population aging and the resulting effects on relative power may create in key cases strong incentives for aggression based on closing window-of-opportunity dynamics. China and Russia are the great powers that are most frequently associated with these predictions. This is not surprising. The aging crisis in both countries are particularly severe—which will likely result in major reductions in relative power in coming decades—and leaders in both possess important revisionist objectives in neighboring regions that are likely to require the use of force to achieve (Eberstadt, 2010; Haas, 2007, pp. 128–131; Wang, 2010, pp. 128–131). Jennifer Dabbs Sciubba, for example, has found that Russia’s increased aggression in neighboring regions between 2006 and 2012 occurred when “Russia’s leaders perceived their country’s decline to be ‘deep’ and ‘inevitable’ because of demographic decline and other political, social and economic strains” (Sciubba, 2014, p. 217).

Similar incentives could soon affect China. China’s relative power in relation to its two strongest rivals in the Pacific, the United States and Japan, has been clearly rising since the end of the Cold War. In 1990, China’s military spending was roughly 4% of America’s and 51% of Japan’s. In 2015, this figure was 36% of America’s and over four and one-half times as much as Japan (Stockholm International Peace Research Institute, 2014). As long as China’s relative power continues to grow, China’s leaders have incentives to avoid crises and allow time to pass as China continues to improve its position. But what happens if the effects of China’s rapidly aging population cause its relative power to plateau and perhaps even decline? If China’s leaders anticipate these outcomes, they will be confronted with very different incentives, including attempting to achieve any revisionist territorial objectives before China’s relative power peaks.

In addition to causing potentially destabilizing shifts in power distributions, a second way based on realist insights in which the costs created by population aging may increase the likelihood of hostilities, and particularly costly hostilities at that, is by pushing states to rely more heavily on nuclear weapons to protect their interests. Because these weapons are viewed by many to be more cost effective than conventional ones, leaders may reason that they offer a way to counter the costs created by aging: With nuclear weapons, states can possess considerable power even in the context of shrinking military budgets. These calculations may push some non-nuclear aging states, such as Japan, to acquire nuclear weapons, and others who already possess this capability to rely more extensively on these weapons as other dimensions of military budgets are reduced.

These outcomes, especially the latter, are fraught with risk.3 The fewer the non-nuclear military options available to a government, the greater the probability that nuclear weapons will be used. This thinking was key to the shift in the United States away from President Dwight Eisenhower’s “massive retaliation” doctrine to President John Kennedy’s “flexible response.” Relying on massive retaliation, critics asserted, left leaders with an unsatisfactory set of choices available to deal with threats: do too little or frequently invoke the nuclear option.

The same logic hold true today. Because of inferior conventional capabilities, Russian leaders in the 2010s have been much quicker to make nuclear threats than in previous decades. As a 2015 report summarized, “A Russian threat to use its nuclear military arsenal [against NATO states if they threatened Russia interests in Crimea or the Baltics] exemplifies how dependent the country is on its nuclear capability to advance its interests . . . The Russian military is presently outclassed by NATO troops in Europe, with less manpower, inferior weapons and fewer allies; hence, a reliance on nuclear scaremongering” (Adamczyk, 2015; also Eberstadt, 2010, pp. 297–298).

Although aging’s effects on power distributions may in some instances increase the likelihood of international conflict, there are also realist-based reasons to expect the opposite outcome. To begin with, if the costs of aging tend to significantly reduce states’ power-projection capabilities for the reasons detailed above, then we should expect less international conflict overall, at least in the long run. Although fluctuations in relative power distributions may create temporary incentives for conflict based on the logic of power transition and window theories, if aging pushes most states to reduce substantially their capabilities and with it their ability to project power abroad, aging is likely to create major incentives for peace over time (Brooks, Brooks, Greenhill, & Haas, 2017).4

The other principal reason why population aging may be likely to increase the probability of international peace based on the insights of realist theories applies to the United States in particular. Like the other great powers, the United States is an aging society. Its median age between 2010 and 2040 is forecasted to increase from 37.2 to 41.2. This change will generate significant costs. According to one prominent study, public spending on the elderly will increase 7.4% of GDP in these years (Jackson et al., 2013, p. 14).

Although the United States is growing older, the scope and pace of America’s aging is less severe than in most other countries, including compared to its competitor great powers: Russia and especially China. America’s median age, for example, is forecasted to be 8 years lower than China’s in 2050 (41.7 years compared to 49.6). The most significant demographic advantage that the United States will enjoy over its rivals is that its working-age population, due to comparatively high fertility and immigration rates, will expand in coming decades while those of Russia and China are forecasted to precipitously decline. Between 2010 and 2050, the number of 15- to 64-year-olds in the United States is expected to grow by 13%, while Russia’s working-age population is predicted to decline by 23% and China’s by 18%.

The United States’ relatively youthful demographics, along with the facts that it has relatively low taxation rates and a comparatively well-funded pension system (OECD, 2016), will help greatly with the fiscal challenges created by social aging. The United States’ growing labor force will contribute to an expanding economy, thereby providing the government with additional revenue to pay for the costs of aging without having to increase taxes, borrow more money, or cut other spending. Moreover, the greatest weakness that the United States has on the aging issue—anticipated massive public expenditures on health care—may not be as high as anticipated. Projected federal health expenditures have fallen considerably based on data provided in 2016 by the Congressional Budget Office and Medicare actuaries. The Center on Budget and Policy Priorities predicts that these expenditures between 2010 and 2046 will increase as a percentage of GDP by roughly 4 percentage points. In 2010, the same organization predicted a rise in these costs of almost 8 percentage points. If the updated forecast is close to reality, the costs of providing for America’s aging population will be considerably lower than many have heretofore predicted (Kogan, Van de Water, & Cho, 2016).

Again, this analysis not mean that the United States will escape the fiscal burdens created by social aging. Rather, as burdensome as the public costs of aging will be for the United States, the public benefits owed to U.S. seniors as a percentage of GDP will likely remain substantially lower than in many of the other great powers. Moreover, the United States will be better positioned to pay for these costs than almost all the other major actors in the system. Global aging will as a result be a powerful force for the continuation of the relative power dominance of the United States.

This means that a power transition involving the most powerful actor in the international system—and all the incentives for aggression that would tend to result from such a change—is unlikely to occur.5 It is this logic that led Haas (2007) to conclude that aging in the great powers is likely to result in a “geriatric peace.” This position ties into core claims of Hegemonic Stability Theory, which asserts that the continued existence of a dominant power is a major source of international peace (Gilpin, 1981).

Aging and Diversionary War Theory

A second set of IR arguments that potentially meshes well with the effects of population aging is Diversionary War Theory, which links domestic crises to an increasing probability of international conflict. To this theory, a common response by governments when their domestic legitimacy is threatened is to engage in aggressive or nationalistic policies. Leaders hope that an international crisis or even the use of force will provide a boost to their domestic support through the “rally-around-the-flag” effect. To this thinking, an international conflict or crisis will diminish domestic discontent as citizens support their government in a conflict with another country (Levy & Thompson, 2010, pp. 99–104).

Population aging could very well result in the kind of domestic stresses that make diversionary conflicts likely. Indeed, the effects of aging both create domestic challenges and make it more difficult for states to deal with other problems. Aging makes existing challenges more difficult to address because states will have to deal with these problems within the context of slowing economic growth and thus likely increasing budget austerity. Aging creates costs by increasing the need for governments to make massive new expenditures for elderly welfare. When governments confront large-scale challenges while simultaneously possessing a reduced capacity to deal with them, the situation is ripe for the activation of the core prediction of Diversionary War Theory: the creation of an international crisis to distract from domestic discontent.

Aging in developing countries like China may be particularly likely to trigger these dynamics. The Chinese government has based its legitimacy to a significant degree on maintaining rapidly rising living standards. Meeting this goal while addressing the major social stresses that frequently come with development—such as environmental decay, urbanization, and rising income inequality—and doing all this within the context of slowing economic growth and while likely adding enormous new expenditures for elderly welfare will be an extremely difficult task. The more Chinese leaders fear that they will be unable to maintain domestic support as budgets become increasingly tight and as economic growth slows, the greater the incentives to adopt aggressive, crisis-seeking, and nationalistic foreign policies in order to boost their domestic position.

It is possible that these dynamics are already in play, as China has adopted more aggressive foreign policies in recent years. Many of these policies, such as assertive actions in territorial disputes with neighboring states, have helped stoke nationalist passions (Cookson, 2015). It is plausible that these trends will intensify as China’s aging crisis becomes more acute.

Aging and Constructivist IR Theories

The core claim of constructivist IR theories is that individuals’ identities are the key source of their policies. An identity answers “Who am I?” It is a subjective assessment of a person’s or group’s defining characteristics and principles (Risse-Kappen, 1996, p. 367; Rousseau, 2006, pp. 4–5, 12, 14). If identities are the principal determinants of policies, different groups with different identities will pursue very different international relations even if other core variables such as power distributions, geography, and other states’ actions remain constant.

Population aging could have major effects on states’ identities, thereby significantly impacting the likelihood of international conflict. Aging could affect identity relationships in two primary ways: It could help bring different identity groups to power or it could activate different identities within an existing group.

Regarding the first of these pathways, it is important to understand that the very act of aging creates identity shifts. To begin with, aging will tend to empower older people at the expense of younger ones: As seniors become a greater percentage of a state’s population, this demographic cohort is likely to have increasing influence on policy making. If true, and if older people tend to have different foreign policy preferences than younger ones, then “older” states will pursue different international relations. In support of this hypothesis, multiple scholars using survey data have found that the elderly tend to possess different foreign policy preferences than younger-age cohorts, including regarding support for international conflict (Brooks et al., 2017; Gelpi, Feaver, & Reifler, 2009, pp. 35–36, 84–88; Feaver & Gelpi, 2004, pp. 125–128, 164, 168, 179, and 174). The older a person is, the less likely it is that he or she will support going to war.6

Population aging is also strongly associated with the rise of another identity group: An increasing number of parents with a small number of children (this trend, which is due to falling fertility levels, is the key cause of societal aging). Parents with relatively few children are likely to see the world quite differently than parents of larger families, with potentially important effects on views of international conflict. Edward Luttwak argues that low-fertility families in the modern era are more casualty sensitive and thus more opposed to war because they are less used to losing children to disease (Luttwak, 1995, pp. 109–122). Brooks, Brooks, Greenhill, and Haas (2017) utilize a different logic and evidence to reach the same conclusion. Their data, which comes from the multi-state, multi-generational “Value of Children” surveys, indicates that the fewer the children parents have, the more that highly valued and non-substitutable psychological and emotional goals (such as having someone to love and care for, enjoyment, self-esteem, gender balance, and carrying on the family name) are tied to each individual child (Arnold & Albores, 1975; Bulatao, 1981, p. 2; Nauck & Klaus, 2007, pp. 487–503). The greater the “value” of any one child, the greater the loss that the child’s death creates, thereby making casualty sensitivity especially high for parents with few children.

In addition to bringing to power different identity groups, population aging is also likely to alter policies by activating different identities at both the elite and societal levels. Unlike the empowerment of the elderly or of parents with few children, however, aging is likely to activate identities that make international conflict more, not less, likely.

Core tenets of constructivist thought are that individuals possess multiple identities and that they will base their actions on which identity is the most salient at a particular time. One of the most important sources of identity activation is threat: Whichever identity is most endangered at a particular time will often be the key source of perceptions and policies (Owen, 2010, pp. 4–5, 38–43; Rousseau, 2006; Wendt, 1999, p. 231). If, for example, a group is being persecuted for its ethnicity, that identity is very likely to be activated. Individuals at this time are likely to perceive themselves and others based on ethnic criteria.

Aging could create major threats to the interests of groups at both the elite and societal levels, thereby activating particular identities that could impact the probability of international conflict. Most obviously, the major economic and fiscal costs created by graying populations can endanger leaders’ ability to stay in power. Threats to elites’ core domestic interests will, in turn, tend to activate their ideological identities, which embody the principles and objectives upon which leaders legitimate their claim to rule. The more leaders fear for their domestic power as the costs of aging accelerate, in other words, the more likely it is that ideology-based principles and goals will be highly salient to their actions, including their international relations (Haas, 2014; Owen, 2010). As a result of these relationships, states’ aging crises could result in periods of increasing ideological polarization, during which elites in one state view others dedicated to similar ideological principles as natural allies and those dedicated to rival ideological principles as enemies.

The severe aging crises in China and Russia, for example, could create substantial threats to Chinese and Russian leaders’ core domestic interests. These threats are the same ones that could push these elites to engage in diversionary conflicts: slowing economic growth and a very tight fiscal environment. Aging, of course, is not the only factor that could endanger leaders’ domestic interests, but its effects both create its own major challenges while making others more difficult to solve.

The more concerned Chinese and Russian elites are about their power at home as their states’ aging problems intensify, the more salient their ideological identities are likely to be to their policies. They are, as a result, likely to increase cooperation with ideological allies, including one another, in order to support their domestic interests, while viewing ideological enemies as increasing threats.

Recent developments potentially support these predictions. Cooperation between China and Russia has significantly increased in recent years, as have statements about the ideological dangers posed by liberal democracies (Haas, 2014, pp. 750–752). This security cooperation has included extensive arms sales from Russia to China, joint military exercises, promises to immediately consult with one another in the event of an external military threat, support of one another’s methods in separatist conflicts (e.g., Chechnya, Xinjiang, Tibet, and Taiwan), and extensive cooperation in the United Nations on a host of issues, including what one scholar labels a “counter-revolutionary proto-alliance” designed to prevent the toppling of governments by popular protests across the Arab world (Baev, 2011, pp. 11–19; Ko, 2006, pp. 203–225). Russian President Vladimir Putin labeled Sino-Russian relations in 2013 a “strategic partnership” and “the best in their centuries-long history . . . They are characterized by a high degree of mutual trust, respect for each other’s interests [and] support in vital issues” (Herszenhorn & Buckley, 2013).

An indicator that ideological similarities play an important role in the two states’ cooperation is the fact that leaders of Putin’s party, United Russia, look at China’s authoritarian political system that allows economic growth as a model that could be best emulated as a result of extensive cooperation and interaction between the two countries (Levy, 2009). Moreover, Chinese and Russian leaders have repeatedly and with increasing frequency described “Western” ideas of liberal democracy as a major subversive threat to the preservation of their domestic interests. As then President Hun Jintao of China wrote in October 2011: “We must clearly see that international hostile forces are intensifying the strategic plot of Westernizing and dividing China, and ideological and cultural fields are the focal areas of their long-term infiltration . . . We should deeply understand the seriousness and complexity of the ideological struggle, always sound the alarms and remain vigilant, and take forceful measures to be on guard and respond” (Wong, 2012).7 In 2014, China’s President Xi Jinping’s called for the creation of a new Asian security structure with Russia that excludes the United States and promotes, according to a summary by the Associated Press, “a political model that pairs autocratic government with a market-oriented economy in defiance of the liberal democratic model” (“China Calls for New Asian Security Structure,” 2014).

If the major domestic stresses caused by population aging contribute to the activation of leaders’ ideological identities and the consequent growth of ideological polarization, the likelihood of international conflict will increase as states’ aging crises intensify. Fears of revolution will tend to push Chinese and Russian elites to view liberal countries like the United States as not only power-based threats, but ideological ones as well because of concerns that these states will be sources of ideological subversion. Moreover, the banding together of ideologically similar regimes in order to protect their shared domestic interests will tend to activate the security dilemma, which is a key source of international conflict according to realist analyses. The more one ideological group tightens its alliance, the more another will be frightened, which will cause the first group to augment its cooperation, and so one. Thus the closer the alignment between China and Russia, the greater the incentives for other countries, such as the United States, Japan, and India, to increase their security cooperation. This incentive will exist even if China and Russia are moving closer together to an important extent due to a product of domestic calculations and the fear of revolution.

In addition to potentially activating leaders’ ideological identities by increasing the dangers to elites’ core domestic interests, population aging can also affect the saliency of different identities at the societal level, especially if various identity groups within the same country are aging at different rates (Jackson & Howe, 2008, p. 184). If, for example, the dominant ethnic group in a country is aging and facing population decline, ethnicity is likely to become highly salient to how members of this group view the world. The result is likely to be growing nationalism and ethnocentrism. We should therefore expect aging populations to frequently become more hostile to minority ethnic groups that are growing as a percentage of a state’s overall population due to either relatively high fertility or immigration levels.

Increasing hostility to immigrant groups in aging states is particularly ironic. Increased immigration is a potential solution to one of the principal costs created by aging: slowing economic growth due to reductions in the number of workers. Yet this solution is likely to be fiercely opposed by many because it will hasten the declining ethnic group’s demise (Kaufmann, 2014; “Why Europe Is Conflicted Over Immigration,” 2015). Aging thus simultaneously creates a need as well as opposition to a principal means of meeting it.

We are likely already currently witnessing these dynamics at work. In many countries throughout Europe and Asia in which the aging problem is particularly acute—and thus the benefits of immigration especially high—anti-immigration sentiments and policies are becoming dominant. Anti-immigration sentiments based on growing ethnocentrism have also fueled recent electoral victories of right parties throughout much of Europe, as well as Donald Trump’s 2016 election. As Amanda Taub, a journalist for The New York Times, summarizes, “White anxiety [with ‘whiteness’ defined ‘as membership in the “ethno-national majority”’] has fueled this year’s [2016] political tumult in the West: Britain’s surprising vote to exit the European Union, Donald J. Trump’s unexpected capture of the Republican presidential nomination in the United States, the rise of right-wing nationalism in Norway, Hungary, Austria and Greece” (Taub, 2016). There are, of course, many potential causes of “white anxiety,” but relative demographic decline due to aging is no doubt an important source of this development.

Increasing nationalism and ethnocentrism could lead to an increased probability of conflict by a number of pathways. Leaders in these circumstances would be more inclined to use force to protect or unify with ethnic kin in other countries, such as Russia in relation to Russian-speaking peoples in Ukraine or the Baltic countries. Or elites could use force to try to stop a source of immigration by members of other ethnic groups. Increasing nationalism could also result in changing patterns of enemies and allies, which could create enhanced opportunities for conflict. A nationalist party in one country is likely to be attracted to fellow nationalists in others. Thus it is not surprising that nationalist leaders in Europe and the United States look far more favorably on President Putin than do other elites. Such sentiments are weakening opposition to sanctions against Russia that were created in response to the 2015 annexation of Crimea, and are perhaps even weakening dedication to the NATO alliance (Brownstein, 2017; Parker, 2016). To the extent that Russia’s leaders possess expansionary international objectives, these outcomes are likely to both enable and embolden aggression.


The preceding analysis has detailed core hypotheses that link population aging to the probability of international conflict, with some predicting a decreased likelihood of international hostilities, others the reverse. To date, there has been a lack of empirical testing of these hypotheses, no doubt in large part because widespread aging is a relatively new phenomenon.

Brooks, Brooks, Greenhill, and Haas (2017) provide the only comprehensive test of which I am aware of the relationship between aging an international aggression. Relying largely on statistical analysis, they find that the relationship between aging and conflict in the post-World War II era is nonlinear. At early stages of aging, states are more likely to become involved in conflict. As the causes and effects of aging accumulate and intensify, however, the probability of aggression is significantly reduced (the aging threshold figures that mark the beginning of the shift to a decreasing probability of aggression are a median age of 20 and an old-age dependency ratio of 8.5%). These findings point to considerable good news for the future of international relations.

The discouraging news is that although aging may be an overall force for international peace in coming years, many of the factors potentially linking aging to an increased probability of aggression are likely to be at work for the two most powerful rivals of the United States and its allies: China and Russia. Aging in these countries could create a dangerous combination of closing windows of opportunity, threats to leaders’ core domestic interests, increasing ideological polarization, and rising ethnocentrism that could make for crisis-prone foreign policies, despite major countervailing incentives for peace.


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(1.) Unless otherwise noted, all demographic data was calculated from United Nations (2015).

(2.) A 2016 study of U.S. states from 1980 to 2010 found that a 10% increase in the percentage of 60-year-olds and over decreased the growth rate of GDP per capita by 5.5% (Maestas, Mullen, & Powell, 2016).

(3.) Scholars debate whether the mere fact of nuclear proliferation is likely to result in a more or less dangerous international system. Some believe proliferation increases the likelihood of peace because of the great deterrent power of nuclear weapons. Others believe the opposite, worrying about miscalculations, accidents, and nuclear custody. On this debate, see Sagan and Waltz (2010).

(4.) It must also be stressed, as Brooks, Brooks, Greenhill, and Haas (2017) do, that some of the dynamics of aging that affect states’ ability to project power abroad that are discussed above are also likely to simultaneously suppress leaders’ willingness to do so. Most notably, as per-unit labor costs for military personnel increase, leaders should be more casualty sensitive and thus more reluctant to use force as they aim to preserve an increasingly valuable resource.

(5.) This claim assumes that the United States will continue to use its relative power advantages to pursue a grand strategy of deep engagement. If the United States possesses the capacity to maintain policies of forward defense yet its leaders choose to pursue a more isolationist grand strategy, regional power transitions could still occur as U.S. forces come home. There is an intense debate in the literature over whether retrenchment policies will in the aggregate benefit or harm U.S. interests (Brooks, Ikenberry, & Wohlforth, 2012). Some argue that the United States should reduce its military presence abroad in favor of “buck-passing” policies, which are ones that are designed to deflect the costs of dangerous tasks to others. To this perspective, even if U.S. retrenchment increases the probability of regional conflicts, these outcomes are unlikely to affect U.S. core interests if local actors can effectively balance neighboring threats. Aging in the United States may increase the salability of these retrenchment policies because “coming home” meshes with the need for the United States to save money in order to pay for the costs created by its own aging problem (Haas, 2007, p. 114). Aging across the great powers may therefore solidify America’s relative power dominance, but America’s own aging problem may still nevertheless help result in a major shift in grand strategy.

(6.) Brooks Brooks, Greenhill, and Haas (2017) attribute these differences in preferences to a combination of biology and political interests. Regarding biology, some scholars have argued high testosterone levels in men contribute to international aggression. If true, then falling testosterone levels due to aging would be expected to weaken inclinations for conflict (Goldstein, 2001, ch. 3; Hudson & den Boer, 2004, pp. 193–195; Rosen, 2004, p. 97). Regarding political interests, the elderly could fairly reason that the more war prone their country’s foreign policies, the less money that will be available for social spending on seniors. Less militaristic policies, in contrast, would increase the likelihood of higher levels of welfare spending. The elderly, in short, confront a major incentive to support pacifist policies that younger-age cohorts do not. These calculations, according to some reports, played an important role in pushing thousands of Japanese pensioners in 2015 to participate in mass protests against Prime Minister Shinzo Abe’s efforts to weaken Japan’s pacifist constitution (Funabashi, 2015). The preceding claims, when looked at from the opposite demographic perspective, also help explain why states with high levels of younger-age cohorts, or “youth bulges,” tend to be violent (Urdal, 2006).

(7.) For other statements about the major ideological threat posed by Western liberal democracies, see Buckley (2013, 2016), Barry and Schwirtz (2012), Wong and Ansfield (2011).