The Future of NATO in the Shadow of the US-Iran War: What Lies Ahead?

The outbreak of the 2026 US–Iran war has once again placed the transatlantic alliance under pressure, but unlike previous crises, its significance lies less in the immediate military implications and more in what it reveals about the internal dynamics of NATO. While the alliance has historically demonstrated resilience in the face of external threats, this conflict has exposed a deeper and structural divergence between the United States and its European allies. Rather than acting as a unified strategic actor, NATO has appeared fragmented, with the United States pursuing a more assertive, interventionist approach, while key European states have adopted cautious and risk-averse positions shaped by economic vulnerability, domestic political constraints, and differing threat perceptions. [1]

The current war has made these tensions more visible and politically consequential. Unlike the post-Ukraine period, which temporarily reinforced transatlantic unity through a shared perception of the Russian threat, the US–Iran conflict highlights the limits of that cohesion when the security priorities of alliance members diverge.[2] Recent reporting points to growing frustration within the United States over European reluctance to fully align with its approach, alongside European concerns about unilateral American decision-making.[3] The result has not been the collapse of NATO, but rather its functional transformation.

This article argues that a potential US-Iran war in 2026 would accelerate NATO’s transformation into a more fragmented and functionally dispersed security arrangement. While the likelihood of the alliance’s dissolution is slim, it is increasingly functioning as a multi-speed structure characterized by varying levels of political cohesion and selective engagement. Understanding this transformation is crucial not only for assessing NATO’s future role by analyzing various future scenarios, but also for anticipating how transatlantic security cooperation will adapt to an increasingly complex and uncertain geopolitical environment.

II. NATO before the War: Unity with Underlying Fractures

Prior to the 2026 US–Iran war, NATO appeared outwardly cohesive, particularly in the aftermath of Russia’s invasion of Ukraine in 2022. That crisis reinvigorated the alliance, leading to increased defense spending, renewed US commitment to European security, and the accession of new members such as Finland and Sweden. At the 2023 Vilnius Summit, allies reaffirmed collective defense as NATO’s core mission and adopted new regional defense plans, signaling a return to deterrence-based unity.[4]

Beneath this apparent unity, however, structural tensions persisted. First, long-standing disagreements over burden-sharing continued to strain transatlantic relations; while European defense spending increased, gaps remained in capabilities and readiness, reinforcing US concerns about unequal contributions.[5] Second, diverging strategic priorities complicated cohesion: the United States increasingly emphasized global competition with China, whereas many European states remained focused on regional stability and risk management.[6] Third, debates over strategic autonomy revealed deeper political fragmentation within Europe itself. Countries such as France advocated for greater European defense independence, while others—particularly in Eastern Europe—remained strongly committed to US leadership within NATO. This internal division limited the EU’s ability to act as a unified security actor alongside NATO.[7] Finally, tensions over decision-making processes persisted. NATO’s consensus-based structure, while ensuring unity, often slowed responses and encouraged informal or ad hoc coalitions outside formal NATO frameworks. These underlying fractures suggest that NATO’s pre-war unity was contingent rather than structural—strong when threat perceptions aligned, but vulnerable when they diverged.

III. The War as a Shock: Divergence in Practice

The current conflict represents a stark revelation of the transatlantic alliance’s realities, highlighting the practical disparities in the responses of its various members. Unilateral US military action marked a major turning point, as Washington acted based on its own strategic priorities without prior coordination or waiting for a consensus among its allies. In contrast, European hesitation and division emerged as defining characteristics of the transatlantic stance, diminishing NATO’s role and rendering it a marginalized institution within the context of this conflict.[8]

Politically, the transatlantic divergence widened due to differing strategic calculations. European capitals did not view the escalation with Tehran from the same American perspective, but rather perceived it as a threat to energy security and a destabilizing factor in their immediate neighborhood. This divergence was not merely a difference of opinion; it manifested practically in the absence of military participation. Most European countries refrained from engaging in the US-led military operations, preferring to remain neutral to avoid involvement in an open conflict that could spill over into their territories or impact their vital interests.[9]

This disparity naturally led to a significant institutional marginalization of NATO. Crucial decisions were not made within the Alliance, and multilateral consultation mechanisms were sidelined in favor of unilateral actions. This profound divergence can be explained by the absence of a shared existential threat. When vital interests are not entirely aligned, national considerations prevail over alliance commitments, which explains Europe’s cautious approach and reluctance to engage militarily in theaters far removed from its primary operational theaters.[10]

IV. Explaining the Divide

The transatlantic divide did not emerge overnight. It is the product of three compounding structural forces whose cumulative weight has made the current divergence not merely predictable, but in hindsight, nearly unavoidable. First, the gap in strategic culture between the United States and Europe has widened to an unprecedented degree. Washington adopts an interventionist approach based on the preemptive projection of military power to protect its global interests, while European states tend toward a strategic culture focused on stability and diplomatic crisis management. This fundamental difference in understanding how security is formulated and achieved has made it difficult to develop a unified military response to a crisis the size of the conflict with Tehran. [11]

Second, economic constraints have played a crucial role in shaping Europe’s hesitant stance. The European continent suffers from extreme vulnerability in the energy sector and is acutely aware that any large-scale conflict in the Middle East will trigger cascading shocks to energy supply chains and prices, exacerbating the risk of inflation and threatening a prolonged economic recession. This pressing economic reality has meant that the cost of engaging in war far outweighs any potential strategic gains, forcing policymakers to prioritize protecting their economies.[12] Third, internal political fragmentation posed a further obstacle to any decisive European action. Many European governments faced electoral pressures and complex domestic politics that made it extremely difficult to sell a new war to their home public. Given these combined factors, divergence was inevitable, as a military alliance cannot function effectively and cohesively when its members have conflicting strategic cultures, differing economic vulnerabilities, and competing political priorities.[13] These structural explanations, however, do not foreclose the future — they define its parameters. The question is no longer, whether NATO will change, but how, and along which of several plausible trajectories that change will unfold.

V. Scenario Analysis: The Future of NATO

Scenario 1: Renewed Cohesion (Low probability)

At first glance, the escalation of the US–Iran war could be expected to reinforce transatlantic unity, particularly if the conflict were to evolve into a direct threat to European security—whether through disruptions to energy flows, missile proliferation, or spillover instability into NATO’s southern flank because, historically, external shocks have often acted as catalysts for alliance cohesion. However, the current trajectory of the conflict suggests that such an outcome remains unlikely. Rather than converging around a shared threat perception, the war has instead exposed—and in many cases deepened—pre-existing divisions between the United States and its European allies. As one report notes, the European response has been characterized by a clear refusal to frame the conflict as a collective Western effort, with the dominant position being that this is not our war.[14] This reluctance reflects not only strategic caution, but also domestic political constraints and economic vulnerability—particularly in the context of energy dependence and recession risks.

At the same time, the US response to European non-alignment has been overtly confrontational, further undermining the conditions necessary for renewed cohesion. President Donald Trump has openly criticized NATO allies for failing to support American military efforts, framing burden-sharing not in terms of collective defense, but in terms of alignment with US strategic priorities. More broadly, the institutional role of NATO itself has been notably limited throughout the conflict. The United States initiated military operations without meaningful consultation within NATO frameworks, and subsequent attempts to involve allies—such as calls to support operations in the Strait of Hormuz—were largely unsuccessful.[15] This sidelining of the alliance weakens the very mechanisms through which cohesion could be rebuilt.

Scenario 2: Multi-Speed NATO (Most likely)

This scenario is based on the fundamental premise that the alliance will not face a dramatic disintegration, but rather a forced functional adaptation that transforms it into a flexible structure capable of accommodating the divergent political wills of its members. In this model, a new security architecture emerges, based on what might be termed pluralism within unity, where the alliance relinquishes its ambition to be a unified strategic actor in favor of becoming a platform that merely provides logistical support and common military standards. Consequently, in practice, selective coalitions will form within NATO’s structure. Countries like Britain and the eastern flank members will choose to pursue full operational and intelligence coordination with American approaches to the conflict, while major European powers such as Germany and France will limit themselves to providing minimal symbolic or political contributions while maintaining independent diplomatic maneuvering. This shift towards fragmented participation may give NATO tactical flexibility in dealing with complex crises, but at the same time it undermines the principle of automatic solidarity and makes collective defense dependent on the convergence of immediate national interests, ultimately turning the alliance into a security supermarket from which members choose what suits their own calculations.

Scenario 3: Strategic Drift / Irrelevance

In this context, the third scenario anticipates a trajectory characterized by the erosion of NATO’s institutional relevance, rendering the alliance not only ineffective but also irrelevant in managing major transnational crises. This view rests on the premise that the precedents set by the US-Iran war—from unilateralism in Washington to structural hesitation in Brussels—will drive actors to systematically circumvent formal alliance frameworks to avoid bureaucratic gridlock or political vetoes. Instead of relying on traditional consultation mechanisms, the centers of gravity for security decision-making will shift to coalitions of the willing and smaller alliances outside the NATO umbrella, leading to a state of institutional atrophy where the alliance’s offices and forces remain, but its real effectiveness evaporates in favor of more flexible and less constrained security arrangements. This strategic drift will inevitably result in the loss of the unified legal and legitimate cover that NATO once provided, leaving European states facing serious security vulnerability. As the credibility of the stable American nuclear umbrella declines, the continent will find itself forced to seek fragmented national or regional security alternatives, ending the era of cohesive collective security and ushering in a new phase of geopolitical fluidity in which the alliance has no leading role.

Scenario 4: European Strategic Autonomy Acceleration

The central driver of this scenario is the growing perception of US unpredictability and unilateralism. The decision to launch military operations against Iran without prior coordination with NATO allies, combined with subsequent pressure on European states to align with US objectives, has reinforced long-standing concerns about the asymmetry of the transatlantic relationship. European reluctance to participate in the war has, in turn, triggered punitive and coercive responses from Washington—including troop withdrawal threats and trade pressure—further eroding confidence in the stability of US commitments.[16] The diversion of US military resources to the Middle East, combined with the prioritization of American strategic interests elsewhere, highlights the vulnerability of European security architectures that remain heavily dependent on external guarantees. In this context, strategic autonomy is no longer framed solely as a political aspiration—particularly by actors such as France—but increasingly as a structural necessity.

At the same time, the war has created both constraints and incentives for European autonomy. On the one hand, economic pressures—including energy shocks and fiscal strain—limit the capacity of European states to rapidly expand defense capabilities. On the other hand, the very same pressures underscore the risks of strategic dependency, potentially accelerating investment in indigenous capabilities and alternative security arrangements. The result is a paradoxical dynamic: short-term constraints coexist with long-term incentives for greater autonomy. Importantly, this scenario does not imply the dissolution of NATO, but rather its transformation into a more asymmetrical and politically fragmented alliance. European states are unlikely to abandon NATO outright, particularly given ongoing threats from Russia. However, they may increasingly seek to hedge against US unpredictability by developing parallel structures, enhancing EU-level defense coordination, and reducing reliance on US military assets over time.

VI. Implications  

The implications of the US–Iran war for NATO extend well beyond the immediate dynamics of transatlantic relations, pointing instead to a broader reconfiguration of the global security architecture. At a systemic level, the conflict reinforces a shift away from formal, institution-based security frameworks toward more flexible and ad hoc coalitions. If NATO is increasingly bypassed in out-of-area conflicts, this suggests a gradual erosion of its role as the primary vehicle for Western military coordination, particularly in crises that fall outside its traditional geographic and strategic scope.

For the United States, this evolution raises fundamental questions about the future of its alliance system. The reliance on unilateral or coalition-based approaches may offer short-term operational flexibility, but it risks undermining long-term alliance cohesion by weakening the expectation of consultation and shared decision-making. Over time, this could lead to a more transactional model of alliances, in which alignment is conditional and issue-specific rather than institutionalized. For Europe, the implications are equally significant. The war underscores both the limits of reliance on US security guarantees and the challenges of developing autonomous strategic capacity. European states are likely to face increasing pressure to define their role in future conflicts—not only in terms of capability, but also in terms of political willingness to act. This may result in a more differentiated European security posture, where some states deepen alignment with the United States, while others pursue greater strategic independence. In this sense, the war accelerates an ongoing transformation in how security is organized, negotiated, and exercised across the transatlantic space.

VII. Conclusion

The 2026 US–Iran war has not precipitated the collapse of NATO, nor has it rendered the alliance obsolete. Rather, it has exposed and accelerated an ongoing transformation in its structure and function. The divergence between the United States and its European allies—rooted in differing threat perceptions, strategic cultures, and political constraints—has revealed the limits of NATO’s cohesion in conflicts that fall outside its traditional framework. What emerges is not a weakened alliance in formal terms, but a more fragmented and functionally differentiated one in practice.

This shift carries important implications for the future of transatlantic security. NATO is increasingly operating as a flexible platform rather than a unified strategic actor, with participation shaped by national interests rather than collective obligation. European governments should develop contingency energy-security frameworks to reduce vulnerability during Middle East crises by diverting from the US’s unpredictability by developing and investing more into parallel structures meant to stabilize the situation should reliance on the US prove volatile in the future administrations as well. The current events and the energy shock could be more easily managed that way, and through a EU-level defense coordination and a reduction on the traditional reliance on US military assets over time, Europe could become more self-sufficient and this would enable it to better absorb the shock of any future crises; what lies ahead is a need to strengthen EU collaboration.

[1] Policy Circle Bureau, “NATO Crisis Deepens over US-Iran War Divide,” Policy Circle, April 2026, https://www.policycircle.org/world/nato-crisis-iran-war-transatlantic-rift/.

[2] North Atlantic Treaty Organization, “Relations with the European Union,” last modified June 20, 2025, https://www.nato.int/en/what-we-do/partnerships-and-cooperation/relations-with-the-european-union

[3] Tuvan Gumrukcu, “Turkey Says US Withdrawal from European Security Architecture Could Be ‘Destructive,’” Reuters, April 18, 2026, https://www.reuters.com/world/turkey-says-us-withdrawal-european-security-architecture-could-be-destructive-2026-04-18/.

[4] North Atlantic Treaty Organization, “Vilnius Summit Communiqué,” July 11, 2023, https://www.nato.int/en/about-us/official-texts-and-resources/official-texts/2023/07/11/vilnius-summit-communique.

[5] Taylor, Kristen, Julia Salabert, and Zak Schneider. “NATO Defense Spending Tracker.” Atlantic Council, last updated April 9, 2026. https://www.atlanticcouncil.org/commentary/trackers-and-data-visualizations/nato-defense-spending-tracker/

[6] Royal United Services Institute, “The Future of the Euro-Atlantic Security Architecture,” RUSI, 2023, https://www.rusi.org/explore-our-research/publications/insights-papers/future-euro-atlantic-security-architecture.

[7] Armin Steinbach, “The EU’s Turn to ‘Strategic Autonomy’: Leeway for Policy Action and Points of Conflict,” European Journal of International Law 34, no. 4 (2023): 973–1006, https://doi.org/10.1093/ejil/chad048.

[8] Nick Schifrin et al., “Trump Lashes Out at NATO Allies over Unpopular Mideast War, Widening Transatlantic Rift,” PBS NewsHour, April 1, 2026, https://www.pbs.org/newshour/world/trump-lashes-out-at-nato-allies-over-unpopular-mideast-war-widening-transatlantic-rift.

[9] EU Leaders Reject Military Involvement in Strait of Hormuz amid War on Iran, Al Jazeera, March 16, 2026, https://www.aljazeera.com/news/2026/3/16/eu-leaders-reject-military-involvement-in-strait-of-hormuz-amid-war-on-iran.

[10] All Bets Are Off: Could Iran War Push US-NATO Ties to Breaking Point? Anadolu Agency, accessed May 2026, https://www.aa.com.tr/en/europe/-all-bets-are-off-could-iran-war-push-us-nato-ties-to-breaking-point/3875932.

[11] Sophia Besch, Erik Brown, and Rafaela Uzan, “Rebalancing the Transatlantic Defense-Industrial Relationship: Regional Pragmatism in Northeastern Europe,” Carnegie Endowment for International Peace, December 2025, https://carnegieendowment.org/research/2025/12/rebalancing-the-transatlantic-defense-industrial-relationship-regional-pragmatism-in-northeastern-europe?lang=en.

[12] Simone Tagliapietra, “How Will the Iran Conflict Hit European Energy Markets?” Bruegel, April 2026, https://www.bruegel.org/first-glance/how-will-iran-conflict-hit-european-energy-markets.

[13] Matthias Matthijs, “Europe’s Disjointed Response to the U.S.–Israeli War With Iran,” Council on Foreign Relations, March 6, 2026, https://www.cfr.org/articles/europes-disjointed-response-to-the-u-s-israeli-war-with-iran.

[14] UK in a Changing Europe, “Not Our War? NATO and the Iran Crisis,” accessed May 5, 2026, https://ukandeu.ac.uk/not-our-war-nato-and-the-iran-crisis/.

[15] Gabriel Gavin, “Trump’s Fury at NATO Allies Deepens Transatlantic Tensions,” Politico Europe, accessed May 2026, https://www.politico.eu/article/donald-trump-anger-nato-allies-europe-united/.

[16] Jakub Krupa, “Trump Threatens to Withdraw US Troops from Italy and Spain,” The Guardian, May 1, 2026, https://www.theguardian.com/world/live/2026/may/01/donald-trump-us-troops-italy-spain-germany-nato-europe-latest-news.