While global attention is increasingly drawn to distant flashpoints—whether to political turmoil in Venezuela, the reach of American power projection across multiple theatres, or the accelerating economic rivalry with China—an unresolved and far more immediate problem continues to fester much closer to home. Europe remains strategically fragmented, politically hesitant, and uncertain about its own capacity to deter threats in its immediate neighbourhood. As Washington’s focus is stretched globally and Europe debates its role within that order, the erosion of NATO’s deterrent credibility on the continent has become a quiet but dangerous reality. The challenge is not the absence of military power, but the failure to consolidate unity, clarity, and resolve where it matters most: within Europe itself.
I. The Return of Deterrence under Grey-Zone Pressure
For more than three decades after the Cold War, deterrence in Europe was largely taken for granted. NATO’s military superiority, combined with the political dominance of the United States, created an environment in which direct challenges to allied territory were widely considered unthinkable. Security debates focused less on territorial defence and more on crisis management, expeditionary missions, and stabilization operations far from Europe’s borders. That strategic comfort has now decisively ended
Since Russia’s invasion of Ukraine in 2022, deterrence has returned to the centre of European security thinking—but in a form far removed from Cold War precedents. Today’s challenge is not a massed armoured thrust across NATO’s borders, but a pattern of persistent, calibrated pressure that deliberately stays below the threshold of open war. Airspace violations by drones and military aircraft, sabotage against critical infrastructure, electronic interference, and information operations have become routine features of the Euro-Atlantic security environment. None of these actions alone constitutes an armed attack. Taken together, however, they raise a far more uncomfortable question: how credible is NATO’s deterrence when the challenge is constant, ambiguous, and incremental?
This is the strategic dilemma confronting the Alliance. Deterrence traditionally rests on clarity—clear red lines, clear attribution, and clear consequences. Russia’s current approach is designed to undermine each of these elements. By operating in the grey zone between peace and war, Moscow seeks to probe NATO’s responses, expose divisions among allies, and gradually normalize a higher level of risk along the Alliance’s eastern flank. The objective is not immediate escalation, but long-term erosion: erosion of confidence, cohesion, and ultimately credibility.
Recent incidents across NATO’s eastern members illustrate this dynamic. Repeated drone incursions into Polish, Romanian, and Baltic airspace, violations involving military aircraft with transponders switched off, and unexplained overflights near sensitive infrastructure have forced allies to respond under conditions of uncertainty. Interceptions are carried out, air defences are activated, and diplomatic protests are issued—but the underlying strategic problem remains unresolved. Each response reassures domestic audiences that vigilance is maintained, yet simultaneously signals to Moscow that such actions can be conducted at a manageable cost.
II. Article 4, Article 5, and the Problem of Ambiguity
At the heart of NATO’s deterrence challenge lies the Alliance’s legal and political framework itself. Article 5 of the Washington Treaty—the cornerstone of collective defence—was designed for a different era. Its language is intentionally narrow, tying collective defence to an ‘armed attack’ against allied territory or forces. This precision was once a strength, anchoring deterrence in unmistakable thresholds. Today, it has become a source of strategic ambiguity.
Most of the provocations NATO faces do not clearly meet the criteria for Article 5. Drone incursions, airspace violations lasting minutes, cyberattacks, and acts of sabotage against civilian infrastructure occupy a legal grey zone. They are hostile, disruptive, and often deliberate—but difficult to classify as acts of war. As a result, NATO’s response mechanism defaults to Article 4 consultations, which allow allies to discuss perceived threats without committing to collective action.
The growing reliance on Article 4 reflects both prudence and weakness. On the one hand, it enables de-escalation and coordination in uncertain situations. On the other hand, it reinforces the perception that NATO lacks a graduated response below the Article 5 threshold. From Moscow’s perspective, this ambiguity is not a flaw to be avoided but an opportunity to be exploited. Each incident tests not only military readiness but political resolve: how far allies are willing to go, how much risk they are prepared to accept, and whether unity holds under sustained pressure.
The inconsistency of responses across member states further complicates deterrence. Some countries, such as Poland and Romania, have adopted more assertive postures, including changes to domestic legal frameworks to allow the interception or destruction of unidentified aerial threats in peacetime. Others remain cautious, emphasizing restraint and legal uncertainty. While understandable given differing threat perceptions and political cultures, this variation weakens the Alliance’s signalling. Deterrence is sustained not merely by military capability, but by predictable patterns of response. When those patterns fragment, the signal sent to an adversary becomes increasingly ambiguous.
Compounding this problem is the broader strategic context. European defence spending has increased since 2022, yet significant capability gaps remain, particularly in air and missile defence, intelligence, surveillance, and rapid reaction forces. NATO has launched initiatives to strengthen its eastern flank, but these measures often appear reactive rather than anticipatory. Exercises and deployments demonstrate readiness, but they do not fully address the underlying question of how the Alliance intends to respond to sustained grey-zone pressure over time.
III. The Credibility Gap and the Future of NATO Deterrence
The cumulative effect of these trends is a growing credibility gap. NATO remains militarily superior to Russia in aggregate terms, combining a vastly larger economy, superior technology, and a network of powerful allied forces, yet deterrence is not measured by balance sheets. It is measured by perception—specifically, the adversary’s belief that aggression will be met with costs that outweigh any potential gain. In the grey zone, that calculation becomes increasingly complex.
Russia’s approach suggests a strategic wager: that NATO’s political caution, legal constraints, and internal divisions will limit its ability to impose meaningful costs for actions below the threshold of war. So far, this wager has not been decisively disproven. Sanctions, diplomatic protests, and symbolic reinforcements may deter major escalation, but they have not halted the steady rhythm of provocations. Instead, they risk normalizing a new baseline of insecurity in which minor violations are tolerated as the price of avoiding major conflict.
This dynamic carries long-term consequences. Deterrence erosion does not announce itself through dramatic failure; it manifests gradually, through the quiet acceptance of what was once unacceptable. Each tolerated incursion slightly shifts the boundary of normalcy. Over time, this can undermine allied confidence, embolden further testing, and increase the risk of miscalculation—precisely the outcome deterrence is meant to prevent.
Addressing this challenge does not require abandoning restraint or embracing reckless escalation. It requires strategic clarity. NATO must articulate—and credibly enforce—a framework for responding to grey-zone aggression that goes beyond ad hoc measures. This includes clearer rules of engagement for airspace violations, stronger collective responses to sabotage and cyber operations, and a willingness to impose costs that are visible, proportional, and politically sustainable.
Equally important is the political dimension. Deterrence cannot be outsourced to procedures or declarations. It depends on shared strategic culture and political will. As long as allies differ fundamentally in their interpretation of risk and responsibility, deterrence will remain uneven. This is particularly sensitive in an era of transatlantic uncertainty, where debates over burden-sharing and long-term American commitment continue to shape European calculations.
‘In deterrence, as in politics, uncertainty can be as dangerous as weakness’
Ultimately, NATO’s deterrence problem is not one of weakness, but of adaptation. The Alliance was built to deter overt aggression in a bipolar world. It now confronts a rival willing to exploit ambiguity, deniability, and gradualism. Whether NATO can adjust its deterrence posture to this reality will shape Europe’s security for years to come.
The question, then, is not whether deterrence still matters—it does—but whether NATO can restore its credibility in an environment where red lines are deliberately blurred. Failure to do so would not result in immediate collapse, but in something more insidious: a slow erosion of confidence that leaves the Alliance reacting rather than shaping events. In deterrence, as in politics, uncertainty can be as dangerous as weakness.
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