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Deterrence theory refers to scholarship and practice on how threats or limited force by one party can convince another party to refrain from initiating some course of action. The topic gained increased prominence as a military strategy during the Cold War with regard to the use of nuclear weapons and is related to but distinct from the concept of mutual assured destruction, which models the preventative nature of full-scale nuclear attack that would devastate both parties in a nuclear war. The central problem of deterrence revolves around how to credibly threaten military action or nuclear punishment on the adversary despite its costs to the deterrer.
Deterrence is widely defined as any use of threats (implicit or explicit) or limited force intended to dissuade an actor from taking an action (i.e. maintain the status quo). Deterrence is unlike compellence, which is the attempt to get an actor (such as a state) to take an action (i.e. alter the status quo). Both are forms of coercion. Compellence has been characterized as harder to successfully implement than deterrence. Deterrence also tends to be distinguished from defense or the use of full force in wartime.
Deterrence is most likely to be successful when a prospective attacker believes that the probability of success is low and the costs of attack are high. The central problem of deterrence is to credibly communicate threats. Deterrence does not necessarily require military superiority.
"General deterrence" is considered successful when an actor who might otherwise take an action refrains from doing so due to the consequences that the deterrer is perceived likely to take. "Immediate deterrence" is considered successful when an actor seriously contemplating immediate military force or action refrains from doing so. Scholars distinguish between "extended deterrence" (the protection of allies) and "direct deterrence" (protection of oneself). Rational deterrence theory holds that an attacker will be deterred if they believe that:
(Probability of deterrer carrying out deterrent threat x Costs if threat carried out) > (Probability of the attacker accomplishing the action x Benefits of the action)
This model is frequently simplified as:
Costs x P(Costs) > Benefits x P(Benefits)
Most of the innovative work on deterrence theory occurred from the late 1940s to mid-1960s. Historically, scholarship on deterrence has tended to focus on nuclear deterrence. Since the end of the Cold War, there has been an extension of deterrence scholarship to areas that are not specifically about nuclear weapons.
A distinction is sometimes made between nuclear deterrence and "conventional deterrence."
The two most prominent deterrent strategies are "denial" (denying the attacker the benefits of attack) and "punishment" (inflicting costs on the attacker).
The use of military threats as a means to deter international crises and war has been a central topic of international security research for at least 200 years.
The concept of deterrence can be defined as the use of threats in limited force by one party to convince another party to refrain from initiating some course of action. In Arms and Influence (1966), Schelling offers a broader definition of deterrence, as he defines it as "to prevent from action by fear of consequences." Glenn Snyder also offers a broad definition of deterrence, as he argues that deterrence involves both the threat of sanction and the promise of reward.
A threat serves as a deterrent to the extent that it convinces its target not to carry out the intended action because of the costs and losses that target would incur. In international security, a policy of deterrence generally refers to threats of military retaliation directed by the leaders of one state to the leaders of another in an attempt to prevent the other state from resorting to the use of military force in pursuit of its foreign policy goals.
As outlined by Huth, a policy of deterrence can fit into two broad categories: preventing an armed attack against a state's own territory (known as direct deterrence) or preventing an armed attack against another state (known as extended deterrence). Situations of direct deterrence often occur if there is a territorial dispute between neighboring states in which major powers like the United States do not directly intervene. On the other hand, situations of extended deterrence often occur when a great power becomes involved. The latter case has generated most interest in academic literature. Building on the two broad categories, Huth goes on to outline that deterrence policies may be implemented in response to a pressing short-term threat (known as immediate deterrence) or as strategy to prevent a military conflict or short-term threat from arising (known as general deterrence).
A successful deterrence policy must be considered in military terms but also political terms: International relations, foreign policy and diplomacy. In military terms, deterrence success refers to preventing state leaders from issuing military threats and actions that escalate peacetime diplomatic and military co-operation into a crisis or militarized confrontation that threatens armed conflict and possibly war. The prevention of crises of wars, however, is not the only aim of deterrence. In addition, defending states must be able to resist the political and the military demands of a potential attacking nation. If armed conflict is avoided at the price of diplomatic concessions to the maximum demands of the potential attacking nation under the threat of war, it cannot be claimed that deterrence has succeeded.
Furthermore, as Jentleson et al. argue, two key sets of factors for successful deterrence are important: a defending state strategy that balances credible coercion and deft diplomacy consistent with the three criteria of proportionality, reciprocity, and coercive credibility and minimizes international and domestic constraints and the extent of an attacking state's vulnerability as shaped by its domestic political and economic conditions. In broad terms, a state wishing to implement a strategy of deterrence is most likely to succeed if the costs of noncompliance that it can impose on and the benefits of compliance it can offer to another state are greater than the benefits of noncompliance and the costs of compliance.
Deterrence theory holds that nuclear weapons are intended to deter other states from attacking with their nuclear weapons, through the promise of retaliation and possibly mutually assured destruction. Nuclear deterrence can also be applied to an attack by conventional forces. For example, the doctrine of massive retaliation threatened to launch US nuclear weapons in response to Soviet attacks.
A successful nuclear deterrent requires a country to preserve its ability to retaliate by responding before its own weapons are destroyed or ensuring a second-strike capability. A nuclear deterrent is sometimes composed of a nuclear triad, as in the case of the nuclear weapons owned by the United States, Russia, the China and India. Other countries, such as the United Kingdom and France, have only sea-based and air-based nuclear weapons.
Jentleson et al. provides further detail in relation to those factors. Proportionality refers to the relationship between the defending state's scope and nature of the objectives being pursued and the instruments available for use to pursue them. The more the defending state demands of another state, the higher that state's costs of compliance and the greater need for the defending state's strategy to increase the costs of noncompliance and the benefits of compliance. That is a challenge, as deterrence is by definition a strategy of limited means. George (1991) goes on to explain that deterrence sometimes goes beyond threats to the actual use of military force, but if force is actually used, it must be limited and fall short of full-scale use to succeed.
The main source of disproportionality is an objective that goes beyond policy change to regime change, which has been seen in Libya, Iraq, and North Korea. There, defending states have sought to change the leadership of a state and to policy changes relating primarily to their nuclear weapons programs.
Secondly, Jentleson et al. outlines that reciprocity involves an explicit understanding of linkage between the defending state's carrots and the attacking state's concessions. The balance lies in not offering too little, too late or for too much in return and not offering too much, too soon, or for too little return.
Finally, coercive credibility requires that in addition to calculations about costs and benefits of co-operation, the defending state convincingly conveys to the attacking state that failure to co-operate has consequences. Threats, uses of force, and other coercive instruments such as economic sanctions must be sufficiently credible to raise the attacking state's perceived costs of noncompliance. A defending state having a superior military capability or economic strength in itself is not enough to ensure credibility. Indeed, all three elements of a balanced deterrence strategy are more likely to be achieved if other major international actors like the UN or NATO are supportive, and opposition within the defending state's domestic politics is limited.
The other important considerations outlined by Jentleson et al. that must be taken into consideration is the domestic political and economic conditions in the attacking state affecting its vulnerability to deterrence policies and the attacking state's ability to compensate unfavourable power balances. The first factor is whether internal political support and regime security are better served by defiance, or there are domestic political gains to be made from improving relations with the defending state. The second factor is an economic calculation of the costs that military force, sanctions, and other coercive instruments can impose and the benefits that trade and other economic incentives may carry. That is partly a function of the strength and flexibility of the attacking state's domestic economy and its capacity to absorb or counter the costs being imposed. The third factor is the role of elites and other key domestic political figures within the attacking state. To the extent that such actors' interests are threatened with the defending state's demands, they act to prevent or block the defending state's demands.
One approach to theorizing about deterrence has entailed the use of rational choice and game-theoretic models of decision making (see game theory). Rational deterrence theory entails:
Deterrence theorists have consistently argued that deterrence success is more likely if a defending state's deterrent threat is credible to an attacking state. Huth outlines that a threat is considered credible if the defending state possesses both the military capabilities to inflict substantial costs on an attacking state in an armed conflict, and the attacking state believes that the defending state is resolved to use its available military forces. Huth goes on to explain the four key factors for consideration under rational deterrence theory: the military balance, signaling and bargaining power, reputations for resolve, interests at stake.
The American economist Thomas Schelling brought his background in game theory to the subject of studying international deterrence. Schelling's (1966) classic work on deterrence presents the concept that military strategy can no longer be defined as the science of military victory. Instead, it is argued that military strategy was now equally, if not more, the art of coercion, intimidation and deterrence. Schelling says the capacity to harm another state is now used as a motivating factor for other states to avoid it and influence another state's behavior. To be coercive or deter another state, violence must be anticipated and avoidable by accommodation. It can therefore be summarized that the use of the power to hurt as bargaining power is the foundation of deterrence theory and is most successful when it is held in reserve.
In an article celebrating Schelling's Nobel Memorial Prize for Economics, Michael Kinsley, Washington Post op‑ed columnist and one of Schelling's former students, anecdotally summarizes Schelling's reorientation of game theory thus: "[Y]ou're standing at the edge of a cliff, chained by the ankle to someone else. You'll be released, and one of you will get a large prize, as soon as the other gives in. How do you persuade the other guy to give in, when the only method at your disposal—threatening to push him off the cliff—would doom you both? Answer: You start dancing, closer and closer to the edge. That way, you don't have to convince him that you would do something totally irrational: plunge him and yourself off the cliff. You just have to convince him that you are prepared to take a higher risk than he is of accidentally falling off the cliff. If you can do that, you win."
Deterrence is often directed against state leaders who have specific territorial goals that they seek to attain either by seizing disputed territory in a limited military attack or by occupying disputed territory after the decisive defeat of the adversary's armed forces. In either case, the strategic orientation of potential attacking states generally is for the short term and is driven by concerns about military cost and effectiveness. For successful deterrence, defending states need the military capacity to respond quickly and strongly to a range of contingencies. Deterrence often fails if either a defending state or an attacking state underestimates or overestimates the other's ability to undertake a particular course of action.
The central problem for a state that seeks to communicate a credible deterrent threat by diplomatic or military actions is that all defending states have an incentive to act as if they are determined to resist an attack in the hope that the attacking state will back away from military conflict with a seemingly resolved adversary. If all defending states have such incentives, potential attacking states may discount statements made by defending states along with any movement of military forces as merely bluffs. In that regard, rational deterrence theorists have argued that costly signals are required to communicate the credibility of a defending state's resolve. Those are actions and statements that clearly increase the risk of a military conflict and also increase the costs of backing down from a deterrent threat. States that bluff are unwilling to cross a certain threshold of threat and military action for fear of committing themselves to an armed conflict.
Main article: Credibility (international relations)
There are three different arguments that have been developed in relation to the role of reputations in influencing deterrence outcomes. The first argument focuses on a defending state's past behavior in international disputes and crises, which creates strong beliefs in a potential attacking state about the defending state's expected behaviour in future conflicts. The credibilities of a defending state's policies are arguably linked over time, and reputations for resolve have a powerful causal impact on an attacking state's decision whether to challenge either general or immediate deterrence. The second approach argues that reputations have a limited impact on deterrence outcomes because the credibility of deterrence is heavily determined by the specific configuration of military capabilities, interests at stake, and political constraints faced by a defending state in a given situation of attempted deterrence. The argument of that school of thought is that potential attacking states are not likely to draw strong inferences about a defending states resolve from prior conflicts because potential attacking states do not believe that a defending state's past behaviour is a reliable predictor of future behavior. The third approach is a middle ground between the first two approaches and argues that potential attacking states are likely to draw reputational inferences about resolve from the past behaviour of defending states only under certain conditions. The insight is the expectation that decisionmakers use only certain types of information when drawing inferences about reputations, and an attacking state updates and revises its beliefs when a defending state's unanticipated behavior cannot be explained by case-specific variables.
An example shows that the problem extends to the perception of the third parties as well as main adversaries and underlies the way in which attempts at deterrence can fail and even backfire if the assumptions about the others' perceptions are incorrect.
Although costly signaling and bargaining power are more well established arguments in rational deterrence theory, the interests of defending states are not as well known. Attacking states may look beyond the short-term bargaining tactics of a defending state and seek to determine what interests are at stake for the defending state that would justify the risks of a military conflict. The argument is that defending states that have greater interests at stake in a dispute are more resolved to use force and more willing to endure military losses to secure those interests. Even less well-established arguments are the specific interests that are more salient to state leaders such as military interests and economic interests.
Furthermore, Huth argues that both supporters and critics of rational deterrence theory agree that an unfavorable assessment of the domestic and international status quo by state leaders can undermine or severely test the success of deterrence. In a rational choice approach, if the expected utility of not using force is reduced by a declining status quo position, deterrence failure is more likely since the alternative option of using force becomes relatively more attractive.
International relations scholars Dan Reiter and Paul Poast have argued that so-called "tripwires" do not deter aggression. Tripwires entail that small forces are deployed abroad with the assumption that an attack on them will trigger a greater deployment of forces. Dan Altman has argued that tripwires do work to deter aggression, citing the Western deployment of forces to Berlin in 1948–1949 to deter Soviet aggression as a successful example.
A 2022 study by Brian Blankenship and Erik Lin-Greenberg found that high-resolve, low-capability signals (such as tripwires) were not viewed as more reassuring to allies than low-resolve, high-capability alternatives (such as forces stationed offshore). Their study cast doubt on the reassuring value of tripwires.
In 1966, Schelling is prescriptive in outlining the impact of the development of nuclear weapons in the analysis of military power and deterrence. In his analysis, before the widespread use of assured second strike capability, or immediate reprisal, in the form of SSBN submarines, Schelling argues that nuclear weapons give nations the potential to destroy their enemies but also the rest of humanity without drawing immediate reprisal because of the lack of a conceivable defense system and the speed with which nuclear weapons can be deployed. A nation's credible threat of such severe damage empowers their deterrence policies and fuels political coercion and military deadlock, which can produce proxy warfare.
According to Kenneth Waltz, there are three requirements for successful nuclear deterrence:
The stability–instability paradox is a key concept in rational deterrence theory. It states that when two countries each have nuclear weapons, the probability of a direct war between them greatly decreases, but the probability of minor or indirect conflicts between them increases. This occurs because rational actors want to avoid nuclear wars, and thus they neither start major conflicts nor allow minor conflicts to escalate into major conflicts—thus making it safe to engage in minor conflicts. For instance, during the Cold War the United States and the Soviet Union never engaged each other in warfare, but fought proxy wars in Korea, Vietnam, Angola, the Middle East, Nicaragua and Afghanistan and spent substantial amounts of money and manpower on gaining relative influence over the third world.
Bernard Brodie wrote in 1959 that a credible nuclear deterrent must be always ready but never used.[a]
Scholars have debated whether having a superior nuclear arsenal provides a deterrent against other nuclear-armed states with smaller arsenals. Matthew Kroenig has argued that states with nuclear superiority are more likely to win nuclear crises, whereas Todd Sechser, Matthew Fuhrmann and David C. Logan have challenged this assertion. A 2022 study by Kyungwon Suh found that nuclear superiority does not reduce the likelihood that nuclear opponents will initiate nuclear crises.
The US policy of deterrence during the Cold War underwent significant variations.
The early stages of the Cold War were generally characterized by the containment of communism, an aggressive stance on behalf of the US especially on developing nations under its sphere of influence. The period was characterized by numerous proxy wars throughout most of the globe, particularly Africa, Asia, Central America, and South America. One notable conflict was the Korean War. George F. Kennan, who is taken to be the founder of this policy in his Long Telegram, asserted that he never advocated military intervention, merely economic support, and that his ideas were misinterpreted as espoused by the general public.
With the US drawdown from Vietnam, the normalization of US relations with China, and the Sino-Soviet Split, the policy of containment was abandoned and a new policy of détente was established, with peaceful co-existence was sought between the United States and the Soviet Union. Although all of those factors contributed to this shift, the most important factor was probably the rough parity achieved in stockpiling nuclear weapons with the clear capability of mutual assured destruction (MAD). Therefore, the period of détente was characterized by a general reduction in the tension between the Soviet Union and the United States and a thawing of the Cold War, which lasted from the late 1960s until the start of the 1980s. The doctrine of mutual nuclear deterrence then characterized relations between the United States and the Soviet Union and relations with Russia until the onset of the New Cold War in the early 2010s. Since then, relations have been less clear.
A third shift occurred with US President Ronald Reagan's arms build-up during the 1980s. Reagan attempted to justify the policy by concerns of growing Soviet influence in Latin America and the regime in Iran, which was established after the Iranian Revolution of 1979. Similar to the old policy of containment, the US funded several proxy wars, including support for Saddam Hussein of Iraq during the Iran–Iraq War, support for the mujahideen in Afghanistan, who were fighting for independence from the Soviet Union, and several anticommunist movements in Latin America such as the overthrow of the Sandinista government in Nicaragua. The funding of the Contras in Nicaragua led to the Iran-Contra Affair, while overt support led to a ruling from the International Court of Justice against the United States in Nicaragua v. United States.
While the army was dealing with the breakup of the Soviet Union and the spread of nuclear technology to other nations beyond the United States and Russia, the concept of deterrence took on a broader multinational dimension. The US policy on deterrence after the Cold War was outlined in 1995 in the document called "Essentials of Post–Cold War Deterrence." It explains that while relations with Russia continue to follow the traditional characteristics of MAD, but the US policy of deterrence towards nations with minor nuclear capabilities should ensure by threats of immense retaliation (or even pre-emptive action) not to threaten the United States, its interests, or allies. The document explains that such threats must also be used to ensure that nations without nuclear technology refrain from developing nuclear weapons and that a universal ban precludes any nation from maintaining chemical or biological weapons. The current tensions with Iran and North Korea over their nuclear programs are caused partly by the continuation of the policy of deterrence.
Since the early 2000s, there has been an increased focus on cyber deterrence. Cyber deterrence has two meanings:
Scholars have debated how cyber capabilities alter traditional understandings of deterrence, given that it may be harder to attribute responsibility for cyber attacks, the barriers to entry may be lower, the risks and costs may be lower for actors who conduct cyber attacks, it may be harder to signal and interpret intentions, the advantage of offense over defense, and weak actors and non-state actors can develop considerable cyber capabilities. Scholars have also debated the feasibility of launching highly damaging cyber attacks and engaging in destructive cyber warfare, with most scholars expressing skepticism that cyber capabilities have enhanced the ability of states to launch highly destructive attacks. The most prominent cyber attack to date is the Stuxnet attack on Iran's nuclear program. By 2019, the only publicly acknowledged case of a cyber attack causing a power outage was the 2015 Ukraine power grid hack.
There are various ways to engage in cyber deterrence:
There is a risk of unintended escalation in cyberspace due to difficulties in discerning the intent of attackers, and complexities in state-hacker relationships. According to political scientists Joseph Brown and Tanisha Fazal, states frequently neither confirm nor deny responsibility for cyber operations so that they can avoid the escalatory risks (that come with public credit) while also signaling that they have cyber capabilities and resolve (which can be achieved if intelligence agencies and governments believe they were responsible).
According to Lennart Maschmeyer, cyber weapons have limited coercive effectiveness due to a trilemma "whereby speed, intensity, and control are negatively correlated. These constraints pose a trilemma for actors because a gain in one variable tends to produce losses across the other two variables."
Intrawar deterrence is deterrence within a war context. It means that war has broken out but actors still seek to deter certain forms of behavior. In the words of Caitlin Talmadge, "intra-war deterrence failures... can be thought of as causing wars to get worse in some way." Examples of intrawar deterrence includes deterring adversaries not to resort to nuclear, chemical and biological weapons attacks or attacking civilian populations indiscriminately. Broadly, it involve any prevention of escalation.
Deterrence theory has been criticized by numerous scholars for various reasons. A prominent strain of criticism argues that rational deterrence theory is contradicted by frequent deterrence failures, which may be attributed to misperceptions. Scholars have also argued that leaders do not behave in ways that are consistent with the predictions of nuclear deterrence theory.
Advocates for nuclear disarmament, such as Global Zero, have criticized nuclear deterrence theory. Sam Nunn, William Perry, Henry Kissinger, and George Shultz have all called upon governments to embrace the vision of a world free of nuclear weapons, and created the Nuclear Security Project to advance that agenda. In 2010, the four were featured in a documentary film entitled Nuclear Tipping Point where proposed steps to achieve nuclear disarmament. Kissinger has argued, "The classical notion of deterrence was that there was some consequences before which aggressors and evildoers would recoil. In a world of suicide bombers, that calculation doesn't operate in any comparable way." Shultz said, "If you think of the people who are doing suicide attacks, and people like that get a nuclear weapon, they are almost by definition not deterrable."
Paul Nitze argued in 1994 that nuclear weapons were obsolete in the "new world disorder" after the dissolution of the Soviet Union, and he advocated reliance on precision guided munitions to secure a permanent military advantage over future adversaries.
As opposed to the extreme mutually assured destruction form of deterrence, the concept of minimum deterrence in which a state possesses no more nuclear weapons than is necessary to deter an adversary from attacking is presently the most common form of deterrence practiced by nuclear weapon states, such as China, India, Pakistan, Britain, and France. Pursuing minimal deterrence during arms negotiations between the United States and Russia allows each state to make nuclear stockpile reductions without the state becoming vulnerable, but it has been noted that there comes a point that further reductions may be undesirable, once minimal deterrence is reached, as further reductions beyond that point increase a state's vulnerability and provide an incentive for an adversary to expand its nuclear arsenal secretly.
Frank C. Zagare has argued that deterrence theory is logically inconsistent and empirically inaccurate. In place of classical deterrence, rational choice scholars have argued for perfect deterrence, which assumes that states may vary in their internal characteristics and especially in the credibility of their threats of retaliation.
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the findings reinforce a key theoretical tenet of the nuclear revolution: Once states have achieved a secure second-strike capability, nuclear superiority does not confer additional political benefits.