Table of Contents

Deterring state adversaries from threatening the core interests, territories, and populations of NATO members lies at the heart of the alliance. If NATO gets this essential mission wrong, the consequences could be catastrophic. To forestall such a possibility, NATO has developed a deterrence posture that includes nuclear and conventional capabilities alongside missile defense and other tools, such as cyber or counterhybrid instruments. Together with exercises and strategic communications, they signal to any potential adversary the alliance’s determination to protect and defend its members.

Two recent events have forced the alliance to tailor deterrence to specific actors. The first was Moscow’s aggression toward Ukraine from 2014 onward, along with its military exercises that rehearsed a war with NATO. The second was the deterioration of the situation in the Middle East and North Africa: civil wars in Syria and Libya and the emergence of the self-proclaimed Islamic State in Iraq and Syria, which helped spawn the 2015 migration crisis. Since then, Russia has remained the focus of NATO’s deterrence, but a reflection is under way on how to best deter nonstate and state threats from the Middle East and North Africa.

Going forward, NATO will need to consider three dimensions of deterrence: who, what, and how. First, the alliance knows that it may be called on to deter other actors in addition to Russia, but it needs to spell out which ones, because each requires a different mix of means and strategies. Second, NATO needs to consider what types of action, beyond armed attacks, it needs to deter. This applies to the full spectrum of threats, including those from Russia. And third, the allies have to constantly review the effectiveness of their current deterrence approaches in all areas of focus, as modern conflict has come to be dominated by unconventional and hybrid tactics used by state and nonstate actors.

Issues at Stake

The Who

On NATO’s Eastern flank, the focus is on Russia. Moscow seeks to achieve its strategic aims—a sphere of influence in the neighborhood and the prevention of NATO’s expansion—without a war but seems ready to engage in brinkmanship and is working on creating favorable conditions to prevail in a conflict. This makes it necessary for the allies to develop a credible deterrence strategy.

Łukasz Kulesa
Łukasz Kulesa is the deputy head of research at the Polish Institute of International Affairs (PISM).

However, NATO also has to deter the threats from states and nonstate entities in the Middle East and North Africa. The effects of conflicts in the region are already being felt on NATO territory, and governments in the most affected member states are asking how they can prevent further spillover of existing and potential crises. The discussions have been light on specifics, though not for lack of options. The allies are already fielding missile defenses in Turkey to defend against missile attacks from Syria; deterring conventional attacks on NATO territory could be the next step, depending on developments in Syria itself. Other actors of concern include Iran, with its growing missile arsenal, and nonstate groups operating in Lebanon, Libya, and Syria.

Farther afield, given the U.S. and other allies’ engagement in the Asia Pacific and NATO’s close links with Australia, Japan, New Zealand, and South Korea, the alliance may have to consider the feasibility of deterring China and North Korea from threatening or harming member states. This would be a new task with significant resource implications and should not be undertaken lightly.

The What

Internally, NATO members need to be clear about specific actions they can reasonably expect the alliance to deter. Clearly, an armed attack—from whatever direction—is one course of action to be deterred, but other actions are not so simple.1

In the case of Russia (and other state actors), the focus is also on deterring coercion: the act of adversaries imposing their will on NATO allies through a combination of military threats and nonmilitary means. For now, the thinking at NATO has emphasized deterrence of a territorial grab or blockade in the Baltic region. However, the characteristics of the Russian approach to warfare mean that the alliance has to look beyond the Baltic Sea and beyond the physical domain, mainly to the cyber realm.2 More and more of the critical systems running hospitals, carrying electricity, or patrolling the skies are now connected to the internet and therefore vulnerable. NATO’s adversaries can, in theory, block allied governments from coming to each other’s aid by threatening devastating cyber attacks that will cause populations to panic and cripple economies.

NATO has already declared that a cyber attack could lead the alliance to invoke its Article 5 collective defense clause, a statement that aims to have a deterrent effect—though there is little evidence that it has stopped adversaries from trying.3 This is mainly because most cyber attacks are designed to stay below the level that would trigger a response of the whole alliance. The allies need a clearer policy on what to do if the line is crossed one day. That policy must also address the thorny issue of credible attribution and should be rehearsed rigorously.

The How

NATO does not need to mirror the activities of its adversaries to deter effectively. The idea is to signal that the alliance will not be intimidated or coerced, but that can be done in multiple ways.

With regard to Russia and the threat of a land incursion, NATO has decided to rely on limited forward deployments along its Eastern flank and on the ability to reinforce quickly those small contingents in times of crisis. The shortcoming of this posture is that if Russia overwhelms the first line of defense, it may be able to use the strength of its conventional forces, as well as the threat of nuclear weapon use, to thwart allied reinforcement.

NATO, as a whole, is adapting its posture to respond, and the United States is strengthening its military presence in Europe to address these potential weak points. The mix of U.S. troops and stored equipment and supplies in Europe is being expanded, including in Poland. And NATO has taken steps to improve its ability to deploy units from North America and move them around Europe by creating a Joint Force Command for the Atlantic and a Joint Support and Enabling Command. Other means of strengthening deterrence include implicit or explicit threats of political or economic sanctions or threats of countermeasures in cyberspace.

Regarding the South, the exact form of deterrence has to match the threat that NATO chooses to deter. With regard to potential state adversaries, NATO’s existing deterrence tools and military capabilities can be utilized against threats from that direction. The creation of the Strategic Direction South Hub—a consultation and coordination body for allies and partners—at the NATO command in Naples, Italy, also contributes to the deterrence mission. However, these measures alone will not deter the main challenge in the South: terrorist groups, with the potential to strike in Europe, operate in lawless spaces.


NATO may be back to its traditional mission of deterrence, but deterrence itself has evolved. A new approach must be adapted to today’s environment, in which a number of deterrence challenges need to be tackled simultaneously and sophisticated nonconventional means can be used jointly with traditional military tools to test the alliance.

Maintain Alliance Cohesion

While the allies’ initial response to deterrence challenges has been impressive, in the long run, deterrence fatigue may present problems. NATO needs to keep all allies committed to the deterrence mission and continue to secure sufficient contributions of committed forces, capabilities, and resources. The risk is that allies’ unity and cohesion—the indispensable foundations of NATO—will weaken as memories of the Islamic State’s caliphate and of Russia’s aggression against Ukraine fade. Adversaries will do their part to sow or exploit divisions or doubts about the strength of solidarity among alliance members.

To keep cohesion from fraying, NATO’s leadership should continuously engage every ally in dialogue about the rationale for the posture, the threat assessment, and members’ views on, and concerns over, the implementation of the deterrence mission. National governments have the same essential responsibility toward their parliaments and publics. NATO must also make sure that discussions do not focus only on one strategic direction but rather address both defense and crisis-management tasks.

Engagement with partners should include a dedicated dialogue on deterrence issues. In some cases, based on mutual consent, NATO should be ready to explore coordinated deterrence signaling or mutually reinforced deterrence activities, such as joint statements, deployments, or exercises.

Engagement with adversaries must be seen as an inseparable companion to deterrence. Dialogue and multiple contact channels remain crucial to convey and receive deterrence signals, avoid accidental or inadvertent escalation, and explore risk-reduction and arms control opportunities.

Deter Russia’s Adventurism

In the foreseeable future, specific challenges connected with deterring Russia will continue to dominate the practical agenda. As a priority, the allies should fully implement the 2018 decisions to adapt NATO’s command and force structure.4 The military credibility of the current deterrence posture depends, to a large extent, on the alliance’s ability to speedily augment its forward-deployed units with follow-on forces.

The allies should look for new ways of stimulating the development of necessary capabilities and interoperability. A more transparent discussion of the major gaps in allied capabilities could help exert pressure on members to make relevant investments. The NATO Military Committee should play a more active role in the alliance’s adaptation by more visibly highlighting the military requirements for credible deterrence to civilian authorities and—via individual military leaders—to NATO populations.

The alliance should continue Article 5–related exercises, especially in more vulnerable regions, as the exercises play a role in deterrence signaling. But NATO must also increase the realism of such exercises to identify the areas where the alliance is lagging behind. The alliance needs more exercises that test mobility, logistics, and the preparedness of infrastructure to transport troops.

NATO’s Enhanced Forward Presence and Tailored Forward Presence strengthen deterrence, but the units deployed need to become a more coherent military force. This calls for further calibrating their combat potential, particularly by adding enablers such as air and missile defense, logistical support, and intelligence, surveillance, and reconnaissance. Flank countries should step up their regional cooperation to help advance that goal.

The process of adapting deterrence is ongoing, and developments on the Eastern flank will require the alliance to constantly reassess its posture. For example, Russia’s deployment of the dual-use SSC-8 cruise missile system and other long-range missiles requires a response.5 On the deterrence track, NATO will need to react to the threat of Russia striking targets away from the border such as harbors, airfields, or command centers, which are crucial for NATO’s ability to deploy its reinforcements. This response should include a mix of bolstering defensive measures and strengthening NATO’s ability to strike back. On the dialogue track, NATO can signal its openness to potential arms control talks.

An additional area that requires attention is the nuclear dimension of NATO deterrence. A more integrated approach to conventional and nuclear planning and exercises is needed. For example, conventional and nuclear exercises should be based on the same scenarios, although not necessarily conducted in the same region or at the same time. NATO needs to walk a fine line by sending deterrence signals to Russia but without suggesting a lowered threshold for the use of nuclear weapons. Fully integrating cyber, space, and information operations into a comprehensive deterrence posture is a less controversial but equally pertinent task.

Deter Unconventional and Hybrid Threats

NATO needs to be careful about defining and signaling its redlines. Making these boundaries too specific could embolden adversaries to intensify their actions below NATO’s declared threshold of response. Being deliberately ambiguous and raising the fear of retribution may be more useful for encouraging adversaries’ self-restraint.

At the same time, NATO should aim to deter specific types of particularly threatening unconventional activities. These include major and sophisticated cyber attacks against allies’ military forces and critical military and civilian infrastructure, proxy military and special forces operations, and state-sponsored terrorism. NATO could declare that such activities may lead it to invoke Article 5 and respond in various ways, including asymmetrically (for example, the response to a cyber attack may not involve only cyber capabilities).

The alliance must be able to identify early whether and when unconventional and hybrid gray-zone actions have become a more substantial and coordinated campaign. In such a case, NATO should aim to deter the adversary from escalating further. This requires increasing the alliance’s capacity to share early-warning intelligence and pool national intelligence-gathering, investigation, and attribution capabilities. NATO should not shy away from attributing ongoing operations to state adversaries, relying on national data as needed. The alliance and its members should be prepared to use direct channels of communication and other means to deliver immediate deterrence signaling in specific cases.

On the Southern flank, NATO faces state actors that use unconventional tactics and proxy forces (for example, Iran and Syria); state collapse and the emergence of ungoverned spaces in Libya, Yemen, and parts of the Sahel; and the activities of a range of nonstate actors, from loose groups to terrorist and criminal networks to highly organized quasi-state structures like Hezbollah. Cooperation with regional partners in addressing these threats will be vital. NATO’s primary task, as elsewhere, should be to deter states in the region from using unconventional tactics against NATO and its allies, using signaling and attribution tools. When possible, the alliance should aim to affect the calculus of nonstate actors to prevent them from harming alliance interests. This may not work with jihadist groups but may be possible with actors motivated by political or economic interests.

Since many of the unconventional threats are not linked to specific regions or actors, a more general approach is called for. The alliance and its members need to continue investing in passive and active measures to neutralize unconventional threats, including in peacetime. Further developing cyber defense and offensive capabilities—NATO’s toolbox for countering hybrid tactics—and strengthening resilience can affect adversaries’ willingness to use unconventional means against NATO and thus help establish deterrence by denial. The toolbox—counterterrorism, special forces, information operations, disruption of terrorist groups’ cyberspace activities—that allies develop for dealing with nonstate and quasi-state entities posing unconventional threats can also be used to deter state adversaries that rely on such tactics.

Encourage Further Debate

For deterrence to work, the allies must clearly communicate their resolve and readiness to respond to an aggressive action. Clear communication is also needed to reassure the allies concerned. At the same time, the alliance faces a challenge in explaining to many citizens of NATO countries the necessity of deterrence. This is especially difficult in the area of nuclear deterrence, where reliance on such destructive weapons remains politically dubious and morally repulsive for many.

Some may suggest that to avoid damaging disagreements, details of the deterrence posture could be kept internal. This would be shortsighted, however. Many measures involved in deterrence, such as replacing dual-capable aircraft, require parliamentary and, therefore, public approval. A continuous open debate on the nature and gravity of the threats, the aims of NATO’s deterrence policy, and the relationship of deterrence to other missions is absolutely necessary.

One opportunity for such debate would be a new strategic concept, if and when the alliance starts work on it. The drafting process usually engages the broad political class and NATO publics. The allies have not revised the document since 2010, mainly for fear that the discussion would be too divisive. But delays carry their own costs, and the alliance is missing an opportunity to discuss why deterrence is necessary and worth the cost.

Deterrence would not cease to be an applicable framework after the start of hostilities. At the expert level, allies should further reflect on how NATO could counter an adversary’s escalation during a conflict and establish intrawar deterrence. This should include exploring concepts of horizontal and vertical escalation and escalation control. The outcomes of such discussions should ultimately inform NATO’s thinking.

The author would like to acknowledge the intellectual contributions of the participants at the workshop on the future of NATO deterrence held at PISM in April 2019 and input from the researchers of PISM’s International Security Program.


1 “Collective defence—Article 5,” NATO, June 12, 2018,

2 Scott Boston and Dara Massicot, “The Russian Way of Warfare: A Primer,” Rand Corporation, 2017,

3 “Wales Summit Declaration,” NATO, September 5, 2014,

4 “Brussels Summit Declaration,” NATO, July 11, 2018,

5 Jacek Durkalec, “European Security Without the INF Treaty,” NATO Review, September 30, 2019,