MD or MAD?: U.S.-Russia Cooperation on Nuclear Disarmament after 9/11 Final Paper for U8565 European Security Professor Cynthia A. Roberts
Yoichiro Sato School of International and Public Affairs firstname.lastname@example.org December 3, 2008
Introduction The nuclear balance between the U.S. and Russia remains an issue. Since the end of the Cold War, the two most powerful nuclear-armed countries have made efforts to reduce nuclear arsenals through bilateral agreements, including the Strategic Arms Reduction Treaty (START) in 1991 and the Moscow Treaty or the Strategic Offensive Reduction Treaty (SORT) in 2002. However, U.S.-Russian nuclear disarmament has not progressed as much as it was expected in the 1990s. In 2009, the START treaty will expire. In addition, the SORT treaty mandates the two countries to accomplish further reduction of their nuclear arsenals by 2012. In spite of these time limits, the negotiations between the two countries move slowly. Why are the U.S. and Russia hesitant to move toward further reductions of nuclear strategic offensive weapons? What prevents U.S.-Russian cooperation on nuclear disarmament in the twenty-first century? This paper argues that 9/11â€™s impact on U.S. threat perception from terrorists and rogue states shifted U.S. nuclear strategy from deterrence to preemption, which made it difficult for the U.S. and Russia to maintain mutual assured destruction (MAD) and to cooperate on nuclear disarmament. Despite the fact that the U.S. and Russia had reduced strategic offensive capabilities during the post-Cold War era, U.S. deviation from the nuclear parity after 9/11 invited Russiaâ€™s concern about U.S. ambition for nuclear supremacy. U.S. missile defense in Europe especially encourages Russia to turn to nuclear rearmament and enhance the possibility of mutual competition of strategic forces. This study aims to contribute to the theoretical discussion on the relationship between nuclear deterrence and missile defense. While the proliferation of weapons of mass destruction to rogue states supporting terrorist groups have drawn much attention since the end of the Cold War in security studies, the U.S.-Russian nuclear balance and the impact of U.S. missile defense on 2
the bilateral strategic relations have been theoretically underdeveloped with few exceptions. 1 However, the progress of U.S.-Russian cooperation on nuclear disarmament is still significant in the twenty-first century because nuclear rearmament between the two countries will increase the costs of U.S.-Russian contingency and the possibility of horizontal nuclear proliferation to other non-nuclear states. To capture difficulties the two countries are currently facing on nuclear disarmament, it is important to analyze 9/11’s impact on U.S. and Russia’s incentives. To examine the issue, I set the following hypothesis:
Hypothesis: The U.S. introduction of missile defense will be likely to make it more difficult for the U.S. and Russia to maintain nuclear parity and to cooperate on nuclear disarmament.
If the U.S. considers the threats from terrorists and rogue states to be significant, it is rational for the U.S. to develop the deployment of missile defense in Europe and Asia. Although U.S. missile defense is imperfect in term of efficacy, the increase in defensive capability will enhance U.S. national security. On the other hand, introducing missile defense in Europe will invite Russia’s concern. If Russia is concerned about the potential of U.S. missile defense to intercept Russia’s ballistic missiles, Russia will be encouraged to deviate from MAD and to develop nuclear offensive capabilities. This paper examines the hypothesis, aiming to capture difficulty of the U.S. seeking the dual policy goals of defending the U.S. homeland from new threats from rogue states and of maintaining strategic stability with Russia through MAD.
For example, Stephen J Cimbala, “Going Ballistic Over Missile Defenses: What Matters and Why,” The Journal of Slavic Military Studies 20 (2007), pp.449-473; Frank C. Zagare, “Reconciling Rationality: A ReExamination of the Logical Foundations of Deterrence Theory,” Journal of Theoretical Politics 16(2004), pp. 107-141.
In the first part, I introduce a theoretical perspective to capture the relationship between nuclear balance between the U.S. and Russia and the impact of U.S. missile defense. In the following part, I describe briefly the history of U.S.-Russian cooperation on nuclear disarmament after the Cold War. In the subsequent part, the paper describes the impact of the 9/11 attacks and changes in U.S. nuclear strategy from deterrence to preemption. In the final part, the paper analyzes the impact of the change in U.S. nuclear strategy on the durability of MAD and U.S.Russian cooperation on nuclear disarmament.
Theoretical Perspective In this part, I introduce game theoretical analyses to capture the changes in strategic relations between the U.S. and Russia after 9/11. Figure 1 shows U.S.-Russian strategic relations before 9/11. Assume the game is one-shot game: both the U.S. and Russia will take actions simultaneously but they will not have the same game again. Also assume the game is a complete information game: both actors know the structure of the game including the other playerâ€™s payoffs. Payoffs represent U.S. utility and Russiaâ€™s utility in order. Both the U.S. and Russia have two kinds of strategy. One is to pursue mutual assured destruction (MAD) without increasing nuclear arsenals. For example, the U.S. can bind herself with the START treaty to limit the number of strategic forces. Another example is that Russia can maintain the ABM treaty to limit the number of anti-ballistic missile facilities. These policies contribute to the maintenance of strategic vulnerability to nuclear attacks from the other player, which will support MAD. The other strategy is to deviate from a MAD situation. For instance, Russia can seek nuclear supremacy by increasing nuclear warheads and developing relevant 4
technology. Similarly, the U.S. can deviate from a MAD situation by abrogating the ABM treaty and introducing missile defense systems. Figure 1 indicates that there are two Nash Equilibria, in which neither the U.S. nor Russia has an incentive to change their strategies. One Nash Equilibrium is the left-upper box in Figure1. At the equilibrium, both countries are willing to seek MAD, and neither country has incentives to change their strategy to unilateral nuclear rearmament (the lower-left box and the right-upper box in Figure 1). The U.S. prefers MAD to nuclear re-armament because the cost of development of nuclear forces is high and Russia is no longer an enemy during the post-Cold War era.
Figure 1: U.S.-Russia strategic relations before 9/11 Russia MAD MAD 3,3* Deviation 2,0
Deviation 0,2 1,1*
Note: * indicates a Nash Equilibrium, in which neither country has an incentive to change its strategy.
Another equilibrium is a situation in which both countries increase strategic forces (the lower-right box in Figure 1). Both the U.S. and Russia deviate from a MAD situation and develop nuclear forces. Neither country has incentives to seek unilateral nuclear disarmament at the equilibrium because unilateral nuclear disarmament would make each worse off (See the lower-left box and the upper-right box in Figure 1). However the situation is not preferable to both countries as much as the maintenance of MAD because both countries suffer from the cost of the rearmament. In the game of Figure 1, the U.S. and Russia can seek a MAD situation, which is Pareto optimal: neither player could further improve his payoff by changing his strategy, without 5
sacrificing the payoff of other players. In a MAD situation, the U.S. and Russia maintain strategic stability by retaining second strike capability. At the same time, both countries can minimize the cost of nuclear forces because they do not invest in unnecessary strategic forces for maintaining MAD. In short, U.S.-Russia strategic situation before 9/11 is stable. However, the structure of the bilateral game changed after 9/11. The U.S. has incentives toward nuclear rearmament, and MAD became unstable. Figure 2 shows the U.S.-Russian strategic situation after 9/11. Because of the terrorist attack in 2001 and potential threats from rogue states, the U.S. became more willing to seek nuclear primacy and to develop missile defense against attacks by terrorists and rogue states. Because the U.S. seeks active defense and preemptive strikes, MAD became less preferable to the U.S.
Figure 2: U.S.-Russia strategic relations after 9/11 Russia MAD MAD 3,3 Deviation 2 + X,0
Deviation 0,2 1+X,1*
Note: * indicates a Nash Equilibrium when the value of X is larger than one.
Figure 2 shows that the identification of Nash Equilibrium is dependent on the value of X. The value of X represents additional utility, which the U.S. finds in deviating from a MAD situation after 9/11. The U.S. finds additional benefit in developing missile defense and in seeking nuclear primacy because threats from terrorists and rogue states became imminent after 9/11. The change in U.S. incentives toward deviation from MAD changes the structure of the game. If the value of X is smaller than one, the U.S. will be still willing to seek MAD when Russia is also seeking for the nuclear parity. Therefore, if the U.S. threat perception from rogue 6
states and terrorists is relatively small, the structure of the game will not change and MAD can be maintained. However, if the value of X is larger than one, the U.S. will be willing to deviate from a MAD situation. If the U.S. threat perception from terrorists and rogue states is significantly large in relatiion to the value of a MAD situation with Russia, the U.S. will be willing to deviate from MAD. The U.S. inclination toward nuclear primacy will invite Russiaâ€™s deviation from MAD as well, which will lead to the Nash Equilibrium of mutual nuclear rearmament (the lower-right box in Figure 2). Figure 1 and Figure 2 show the change in U.S.-Russian strategic relations after 9/11. U.S. threat perception of terrorists and rogue states after 9/11 and U.S. incentives toward nuclear primacy and missile defense made it difficult for the strategic rivals to maintain a MAD situation. In the post-9/11 period, the U.S. and Russia became more willing to seek nuclear rearmament.
U.S.-Russian cooperation after the Cold War During the Cold War, the U.S. and the Soviet Union developed bilateral frameworks. In 1972, the two powerful nuclear countries agreed on the Anti-Ballistic Missile Treaty (ABM treaty), which limited the number of anti-ballistic missile sites. In 1987, the Intermediate-Range Nuclear Forces was agreed upon, which eliminated nuclear and conventional ballistic and cruise missiles with 500-5,500 km ranges in Europe. In addition, the two countries started in 1982 bilateral negotiations aimed at massive reductions in strategic forces. As a result, in 1991, the two countries agreed on the Strategic Arms Reduction Treaty (START I), which was aimed at 7
banning more than 6,000 nuclear warheads atop of total of 1,600 ICBMs, SLBM, and air bombers. After the Cold War, the two nuclear powers developed cooperative relations on nuclear disarmament. The U.S. and Russia implemented the obligation of the START treaty, resulting in the removal of about 80% of their strategic forces.
Furthermore, the two biggest nuclear
retainers agreed on the Moscow Treaty or Strategic Offensive Reduction Treaty (SORT) in 2002, which encourages the two parties to further limit nuclear arsenals to 1,700 – 2,200 deployed. The U.S. and Russia have cooperated not only nuclear disarmament but also other issues. In 1997, U.S. President Clinton and Russian President Yeltsin agreed on the establishment of the Russian–American Observation Satellite (RAMOS) system, which was aimed to share warning of missile attacks.2 Both countries hoped that increasing transparency between the strategic rivals discourage contingency of nuclear war. Although the program was not intended to link with other military satellites in space, the project was aimed at developing trustful relations and future further cooperation on nuclear balance. 3 The U.S. and Russia launched another cooperative project. In 1998, U.S. President Clinton and Russian President Yeltsin announced a “Joint Statement on the Exchange of Information.” The statement hoped to increase transparency and to promote mutual confidence regarding information on ballistic missiles. Based on the statement, Russian President Putin and U.S. President Clinton agreed on a memorandum of agreement on establishing Joint Data Exchange Center (JDEC) in June 2000.4 The agreement of JDEC states in Article 1 that the exchange center provides data from early warning systems and notifications of missile launches
Victoria Samson, “Prospects for Russian-American Missile Defence Cooperation: Lessons from RAMOS and JDEC,” Contemporary Security Policy 28.3 (2007), p.494. 3 Ibid, p.497. 4 Ibid, p.503. 8
with each other.5 The agreement set series of phases as test periods for 100 days, in which both countries would start test of exchange procedures, equipments, and software.
The impact of 9/11 The 9/11 attacks strengthened the U.S. perception of threats from terrorists and rogue states supporting terrorist activities. The impact of the terrorist attacks shifted U.S. nuclear strategy from deterrence to preemption and encouraged the U.S. to deploy missile defense systems in the U.S. homeland and allies’ territories. In January 2002, U.S. Department of Defense submitted the summary of Nuclear Posture Review to U.S. Congress. The U.S. had reviewed its nuclear strategy first time since the last time of 1994.6 The report emphasized the importance of missile defense: •
Missile defense is most effective if it is layered; that is, able to intercept ballistic missiles of any range in all phases of their flight.
The United States seeks effective defenses against attacks by small numbers of longer range missiles as well as defenses against attacks by larger numbers of short- and medium-range missiles.
Missile defense systems, like all military systems, can be less than 100-percent effective and still make a significant contribution to security by enhancing deterrence and saving lives if deterrence fails.7
White House. “Memorandum of Agreement between the United States of America and the Russian Federation on the Establishment of a Joint Center for the Exchange of Data from Early Warning Systems and Notifications of Missile.” June 4, 2000. Available at http://www.fas.org/nuke/control/jdec/text/000604-warnwh3.htm (Accessed on December 1, 2008) 6 Nuclear Posture Review. January 8, 2002. The Excerpts are available at http://www.globalsecurity.org/wmd/library/policy/dod/npr.htm. 7 Ibid.
The review also mentioned that while the U.S. should seek cooperative relations with Russia in terms of nuclear disarmament the U.S. should be prepared for the contingency with the former rivals: Russiaâ€™s nuclear forces and programs, nevertheless, remain a concern. Russia faces many strategic problems around its periphery and its future course cannot be charted with certainty. U.S. planning must take this into account. In the event that U.S. relations with Russia significantly worsen in the future, the U.S. may need to revise its nuclear force levels and posture.8 Although the report suggested that the U.S. can maintain the size and level of strategic forces under the obligation of the Moscow Treaty for the time being, the review warned that the U.S. could not be optimistic about the future cooperation on nuclear disarmament. In September 2002, the U.S. government laid out a more comprehensive security strategy. The National Security Strategy emphasized the importance of preemption, comparing terrorist threats and threats in the Cold War:
In the Cold War, especially following the Cuban missile crisis, we faced a generally status quo, risk-averse adversary. Deterrence was an effective defense. But deterrence based only upon the threat of retaliation is less likely to work against leaders of rogue states more willing to take risks, gambling with the lives of their people, and the wealth of their nationsâ€Ś The United States has long maintained the option of preemptive actions to counter a sufficient threat to our national security. The greater the threat, the greater is the risk of inactionâ€” and the more compelling the case for taking anticipatory action to defend ourselves, even if 8
uncertainty remains as to the time and place of the enemy’s attack. To forestall or prevent such hostile acts by our adversaries, the United States will, if necessary, act preemptively.9
Declaratory policy emphasizing preemption and missile defense was carried out immediately. Donald Rumsfeld was appointed as Secretary of Defense by President Bush. Rumsfeld had initiated a commission, which had concluded a report to support the deployment of missile defense in 1998.10 In addition, The Bush administration abrogated the ABM treaty in July 2002, which had limited anti-ballistic missile systems and maintained the vulnerability to second strikes. Although previous U.S. administrations had developed missile defense systems, the 9/11 attacks had huge impact to drive the Bush administration to accelerate the development of missile defense. The Reagan administration had launched Strategic Defense Initiative during the Cold War, and a missile act was signed in U.S. Senate and Congress during the Clinton administration.11 However, the Bush team placed missile defense at the top of policy agenda. The Bush administration crystallized missile defense policy through National Security Presidential Directives-23 (NSPD-23), in December 2002, aiming at the deployment of PAC-3 and other measures to intercept ballistic missiles by the beginning of 2004.12 By 2008, the U.S. had placed missile defense systems in Alaska and California and agreed on deployment of interceptors and radar sites with several U.S. allies, such as Japan, the 9
The White House. “National Security Strategy of the United States of America” September 2002. Available at http://www.whitehouse.gov/nsc/nss/2002/nss.pdf (accessed on November 30, 2008.) 10 Bertel Heurlin, “Missile Defence in the United States,” in Bertel Heurlin and Sten Rynning, eds., Missile Defence: International, Regional and National Implications (New York: Routledge, 2005), p.64. Also, see “Report of the Commission to Assess the Ballistic Missile Threat to the United States,” July 15,1998, Available at http://www.fas.org/irp/threat/missile/rumsfeld/charter.htm 11 Ibid. 12 The White House. “National Security Presidential Directives-23 ” December 2, 2002. Available at http://www.fas.org/irp/offdocs/nspd/nspd-23.htm (Accessed on November 20, 2008) 11
Czech Republic and Poland. Also, Britain gave permission to the U.S. to use the radar sites at Flyingdales as an early warning radar system.
Back to Strategic Rivals after 9/11 The shift of U.S. nuclear strategy from deterrence to preemption and developing missile defense systems gave Russia incentives to deviate from MAD. Although Russia made efforts to maintain cooperative relations with the U.S., those efforts did not result in the maintenance of MAD. There are several issues that have made it difficult for the U.S. and Russia to develop nuclear disarmament and to sustain MAD. First, there are legal issues regarding a bilateral framework on nuclear disarmament. In 2002, the U.S. and Russia agreed on the Moscow Treaty or the SORT treaty to limit strategic arsenals between 1,700 and 2,200. However, SORT has no provision to monitor nuclear reduction processes. Facing the expiry of START in 2009 and the lack of provisions for verification and monitoring in SORT, two countries are now facing a time limit to re-establish legal framework to implement the obligation of the treaty. Second and more importantly, the U.S. and Russia have not been successful in building trustful relations regarding U.S. missile defense systems in Europe. In 2000, a former Minister of Foreign Affairs of Russia Sergei Ivanov warned that America’s plans of deploying antiballistic missile systems, which was prohibited by the Anti-ballistic Missile (ABM) treaty, would gravely concern Russia and many other countries.13 In the light of Russia’s opposition to missile defense, the U.S. attempted to remove Russia’s concern, briefing that missile defense systems aim to 13
Sergei Ivanov, “The Missle-Defense Mistake: Undermining Strategic Stability and the ABM Treaty,” Foreign Affairs 79 (September/October 2000), pp.15-20
intercept ballistic missiles not from Russia but from rogue states, such as Iran and North Korea. Furthermore, the U.S. did not accept a Russia’s proposal that the U.S. and Russia share missile sites in southern Russia and Azerbaijan.14 Russia’s concerns about U.S. missile defense are “legitimate.” According to Theodor A. Postol, U.S. missile defense systems in Europe could intercept ballistic missiles from Russia. 15 However, the U.S. has not succeeded in persuading Russia that U.S. missile defense in Europe would not threaten Russia’s national security. At the Sochi summit between Bush and Putin in April 2008, the two countries announced the continued disagreement over the missile defense issue. In August 2008, Russia’s invasion on Georgia encouraged the U.S. to deploy missile defense systems in Europe, resulting in the agreement with Poland just after the invasion. Although there had been several projects for U.S.-Russian cooperation on nuclear disarmament and missile defense, these projects lost momentum during the Bush administration. As mentioned above, the U.S. and Russia had agreed to start the project of the Russian American Observation Satellite (RAMOS) for early warning information sharing in missile defense. The project was aimed to assure that neither country was under attack of ballistic missiles by launching space satellites. Despite the two countries having implemented a series of experiments in the RAMOS framework, the project was terminated in 2004. 16 One reason for the termination of the project is that Russia was concerned about the budgetary limitation: Russia was not able to provide thirty million dollars annually for the symbol of U.S.-Russian cooperation. 17 The U.S. 14
Stephen J Cimbala, “Going Ballistic Over Missile Defenses: What Matters and Why,” The Journal of Slavic Military Studies 20 (2007), pp.449-473. 15 Theodor A. Postol, “Proposed U.S. Missile Defense in Europe: Technological Relevant Issues to Policy, ” a presentation given at the American Association for the Advancement of Science in Washington, DC, 28 Aug. 2007, available at http://cstsp.aaas.org/content.html?contentid=1175 (Accessed on December 1, 2008). 16 Alla Kassianova, “Roads Not (Yet) Taken: Russian Approaches to Cooperation in Missile Defense,” In Berrel Heurlin and Sten Rynning eds., Missile Defence: International, Regional, and National Implications, (New York: Routledge, 2005), p. 97. 17 Victoria Samson, “Prospects for Russian-American Missile Defence Cooperation: Lessons from RAMOS and JDEC,” Contemporary Security Policy 28.3 (2007), p.501. 13
also became hesitant to continue U.S. commitment to the expensive project for missile defense cooperation. 18 Another area of cooperation between the U.S. and Russia was the Joint Data Exchange Center (JDEC). The U.S. and Russia agreed to exchange warning data through establishing the center in Moscow, and the two sides agreed on rules for the implementation of the program. However, the first trial of exchanging data was postponed in 2001. The U.S. and Russia had disputes over which side should pay the tariff and tax of equipments of the projects. Even after the U.S. and Russia agreed on the SORT treaty in 2002, Russia was not able to continue this project: the Russian fiscal system did not allow them to pay the tax and the costs of the program.19 The disagreement on U.S. missile defense encouraged Russia to develop nuclear capabilities. After Russia observed the low probability of the bilateral cooperation in missile defense, Russia is seeking nuclear advantage, modernizing strategic forces. Russia is currently upgrading the three nuclear parts of ICBMs, SLBMs and Bombers, and it is estimated that Russia’s nuclear capability will exceed U.S. nuclear forces in 2025 (See Table 1).20
Table 1: Comparison of U.S. and Russian Force Structure in 2008 and 2025 Adopted from the table in Thayer and Skypek 2008, p. 65. The United States Russia ICBMs SLBMs Bombers Total ICBMs SLBMs Bombers 2008 450 288 72 810 430 176 79 2025 225 225 40 490 350 225 90
Total 685 665
Victoria Samson, “Prospects for Russian-American Missile Defence Cooperation: Lessons from RAMOS and JDEC,” Contemporary Security Policy 28.3 (2007), pp.501-502. 19 Victoria Samson, “Prospects for Russian-American Missile Defence Cooperation: Lessons from RAMOS and JDEC,” Contemporary Security Policy 28.3 (2007), pp.506-507. 20
Bradley A Thayer and Thomas M. Skypek, “Russia Goes Ballistic,” The National Interest 97 (September/October 2008), pp. 65.
Now Russia’s intention to develop countermeasures against U.S. missile defense is revealed clearly. In December 2008, Russian chief of strategic missile forces announced that Russian ICBMs would be modernized to penetrate U.S. missile defense systems. The chief announced that Russia would develop RS-24, a new ICBM with MIRVs to overcome U.S. missile defense.21 U.S. deployment of missile defense and Russia’s nuclear rearmament can destroy the nuclear parity, which had been maintained since the end of the Cold War. Although U.S. interceptors, such as Pac-3, have not proved that they can protect the U.S. homeland from any ballistic missiles with decoys, missile defense systems theoretically can induce Russia and other nuclear powers to develop offensive capability and equal missile defense systems.22 Therefore, the U.S. shift in nuclear strategy from deterrence to preemption and the introduction of missile defense enhanced the possibility of nuclear rearmament of the U.S. and Russia
Conclusion This paper demonstrates that the impact of the 9/11 attacks reminded the U.S. of the importance of updating its nuclear strategy, which led to a preemptive strike strategy and the deployment of U.S. missile defense systems in Europe. Although the U.S. and Russia had cooperated on nuclear disarmament through bilateral agreements, such as START and SORT after the Cold War, U.S. deviation from MAD made it difficult to implement the goals of the bilateral regimes.
The Associated Press, “Russia; Countering U.S. Missile Plans,” in New York Times, December 2, 2008, available at http://www.nytimes.com/2008/12/02/world/europe/02briefs-COUNTERINGUS_BRF.html. 22 Frank C. Zagare, “Reconciling Rationality: A Re-Examination of the Logical Foundations of Deterrence Theory,” Journal of Theoretical Politics 16(2004), pp. 107-141.
The U.S. missile defense especially became an obstacle for the two countries to maintain nuclear parity and to seek nuclear disarmament. The game theoretical models show that neither player had an incentive to maintain MAD when the U.S. started the deployment of its missile defense. The theoretical suggestion that the model implies was observed empirically. Septermber 11, 2001, was the turning point for the U.S. to start considering seriously the potential of missile defense in order to cope with threats from rogue states and terrorists. To meet the dual objectives of maintaining strategic stability with Russia and defending the homeland from terrorists, the U.S. launched projects to cultivate cooperation with Russia. However, RAMOS and JDEC ended without remarkable achievement. Rather, the failure of the bilateral cooperation led to Russiaâ€™s concern about U.S. missile defense, and Russia is seeming to turn to nuclear rearmament by modernizing strategic forces. The hypothesis that this paper poses is theoretically and empirically supported. However, the possibility of U.S.-Russian cooperation on nuclear disarmament should be further examined by an alternative hypothesis. For example, it could be argued that the level of leadership and commitment of the two countries can influence the bilateral cooperation on nuclear disarmament. It can be examined, for instance, whether U.S. nuclear strategy pursued by the next administration will influence the possibility of cooperation. On the other hand, the relationship between missile defense and nuclear balance should be further examined by other case studies. For example, the U.S. introduction of missile defense in Asia can deteriorate the nuclear balance between the U.S. and China. Although China does not have equal strategic capabilities to U.S. capabilities, the future nuclear balance can be influenced by U.S. missile defense deployed in Japan. Future research can address this case for theoretical purposes. 16