The post-Cold War nonproliferation order is unraveling, replaced by an era of strategic entropy—a condition where deterrence dynamics are no longer predictable, alliances are no longer immutable, and nuclear restraint is no longer assured. As U.S. extended deterrence faces growing skepticism and allies reconsider their reliance on Washington’s nuclear umbrella, the strategic environment is shifting toward a multipolar, fragmented nuclear order. If current trends continue, what was once an ironclad nonproliferation regime will give way to an unstable global landscape where independent nuclear actors, unchecked proliferation, and unpredictable escalation become the defining features of international security.

Since the 2014 Russian annexation of Crimea, nuclear tensions have been increasing globally, especially among the US, Russia, and China. First, the termination and cancellation of various arms control treaties between the US and Russia in 2019 and 2023, along with the PRC’s long-held aversion towards engaging in arms control dialogue more generally, has led to renewed nuclear rearmament efforts and the emergence of a multipolar nuclear environment 1. Second, ongoing PRC arsenal expansion efforts aimed at rivaling the strategic forces of the US and Russia have been met in kind by existing (and proposed) US nuclear modernization programs, further exacerbating geopolitical tensions 2. Pairing these trends with the rise of a revisionist China and the palpable threat of revanchist Russia, along with the persistent presence of a nuclear North Korea and Iran approaching the atomic threshold, the nuclear environment is seething.

The confluence of these three trends has not only increased the global threat of nuclear crises or conflict but also led to an increased appreciation for nuclear deterrence dynamics and an ascending reliance on nuclear assurance amongst American allies. Yet, growing sentiments of security malaise and strategic variability with NATO’s strategic posture have uprooted the traditional strategic resolve championed by the US and extended to the thirty-plus “allies and partners” relying on the extended deterrence of the American nuclear umbrella 3. Fluctuant foreign policy and inconsistent engagement doctrines across volatile presidential election cycles have aroused allied ambiguity over an uncertain US defense policy environment.

The ascension of the second Trump administration and Washington’s renewed ‘America First’ transactional approach to commitments with the Transatlantic alliance has further augmented allied apprehensions regarding American nuclear assurances. Vocal calls by officials in Washington for the strategic disengagement away from US foreign nuclear security guarantees have been met in kind by calls in European capitals for overhauls to defense spending and even strategic autonomy 4. Rather than building ‘burden sharing’ amongst allies, this paradigm shift by President Trump may entrench European and allied countries’ ‘burden-shifting’ away from US guarantees to allied or even novel domestic nuclear weapons programs – further solidifying the shuttering of the American nuclear umbrella.

Amidst the uncertainty surrounding the US nuclear-extended deterrence, France has reinserted itself into the strategic debate. French President Emmanuel Macron’s recent statements proposing an expansion of its nuclear deterrent to protect European allies from the Russian threat have gained popularity over the last week 5. Although French nuclear doctrine is principally conceived to protect French “vital interests”, France’s vital interests have been broadened since 2020 to encompass a “European dimension” and are not necessarily limited to French borders, according to French President Macron and the Armed Forces Minister 6. The duo made the case for a French extended deterrence against Russia more explicit last week, describing Russia as a “threat to France and Europe” and proclaiming that “Europe’s future does not have to be decided in Washington or Moscow” 7. Yet, France’s proposal holds the potential to further deteriorate the nonproliferation regime and expedite nuclear entropy in Europe and beyond. Supplanting the US nuclear umbrella with a French arsenal of deterrence brings with it escalatory risks due to France’s nuclear doctrine – allowing for first-use strikes or nuclear warning shots – and force size and composition, which at ~290 warheads is some seventeen times smaller than that of the US or Russia 8. Further complicating measures is the popularity of the French proposal amongst European leaders like those of Germany, Lithuania, Poland, and Latvia 9.

Consequently, replacing the US nuclear umbrella with the French arsenal, even with the addition of the UK’s strategic forces, would leave Europe and NATO with an immediate imbalance of forces favoring Moscow. Although potentially effective as a stop-gap measure, the more aggressive French doctrine, along with a more expansive nuclear force-sharing umbrella, would increase the risks of nuclear miscalculation, crises, and war. Such an imbalance would also incentivize these and other American allies to pursue their own nuclear weapon programs to replace the loss of nuclear assurance from a US disengagement.

European capitals are actively reevaluating nuclear-sharing arrangements, expanding conventional deterrence, and, in more extreme cases, entertaining the possibility of indigenous nuclear capabilities 10. In East Asia, similar pressures are mounting as South Korea, Japan, and Australia intensify high-level consultations with Washington on nuclear posture, seeking more explicit guarantees or greater nuclear access 11. These recalibrations risk accelerating a cascading proliferation effect in which the perceived fragility of extended deterrence compels one state after another to reconsider the nuclear option—ultimately eroding the long-standing barriers that have constrained nuclear diffusion since the Cold War. If left unchecked, this systemic unraveling of nonproliferation norms could usher in an era of strategic entropy, where nuclear arsenals multiply, alliance cohesion weakens, and the risk of crisis escalation grows exponentially.

The question is no longer whether U.S. allies should seek alternative nuclear deterrence arrangements but rather when and how they will do so if current trends persist. Should the trends in the strategic environment continue to converge, along with a continued acceleration of the Trump-era burden-shifting, allies will inevitably explore alternative options, whether by deepening nuclear ties with the UK and France or by pursuing indigenous nuclear capabilities outright.

As Russia continues to brazenly disregard international law and China increasingly challenges U.S. extended deterrence in the Indo-Pacific, any shift in Europe’s nuclear posture risks compounding existing geopolitical volatility 12. Any shift toward greater nuclear autonomy among U.S. allies—whether through reinforced extended deterrence arrangements or independent nuclear programs—risks triggering a broader cascading effect. A more autonomous European deterrent—whether through France’s proposed nuclear umbrella or a broader realignment of NATO’s nuclear architecture—would not occur in a vacuum. Instead, it could set off a chain reaction of strategic recalibrations, where other regional powers seek to justify the expansion of their own deterrence arrangements or, in more extreme cases, pursue independent nuclear capabilities outright.

As European nations reconsider their reliance on American nuclear assurances, other regional powers may view this as a precedent for strengthening their own deterrence frameworks or even embarking on indigenous nuclear weapons programs. Once a single U.S. ally moves beyond the traditional constraints of the nonproliferation regime, others—previously firm supporters of nonproliferation norms—may feel compelled to follow suit in pursuit of their own security interests 13. A precedent set in Europe could resonate well beyond the Transatlantic theater, emboldening states in East Asia and the Middle East to reconsider long-standing nonproliferation commitments 14. This domino effect would be particularly acute in regions like East Asia and the Middle East, where long-standing security arrangements are already under strain.

If allies conclude that U.S. commitments are no longer an immutable pillar of their defense, the strategic environment could rapidly devolve into a multipolar nuclear order, where nuclear arsenals proliferate not as deliberate strategic choices but as reactive necessities. In this way, the reconfiguration of the world into a multipolar order likewise necessitates the transformation of nuclear proliferation into a global process. If nuclear reliance among U.S. allies shifts from Washington to alternative security structures, or if new nuclear actors emerge under the guise of self-reliance, the strategic environment would become increasingly fragmented and unstable—further eroding the credibility of existing arms control frameworks and amplifying the risk of multi-front proliferation cascades. Should this dam of nonproliferation break, the relative power and influence of the United States would erode, diminishing Washington’s ability to shape global security and reinforcing the new era of strategic entropy 15.

The unchecked spread of nuclear weapons—even among U.S. allies—fundamentally weakens American geopolitical power and undermines its ability to shape the global order. The United States has long benefited from a system where nuclear deterrence was centralized within its arsenal and a handful of allied partners, allowing Washington to dictate escalation dynamics, enforce strategic stability, and maintain leverage over adversaries and allies alike. But as more nations seek nuclear capabilities—whether in response to U.S. retrenchment or as a hedge against rising multipolar threats—this once-unilateral advantage is eroded.

Nuclear diffusion does not merely redistribute power to Washington’s allies; it also emboldens new nuclear actors, who, unconstrained by U.S. oversight, may wield their arsenals in pursuit of regional grievances or unilateral strategic aims 16. The rise of independent nuclear forces within NATO, East Asia, or the Middle East would complicate Washington’s ability to exercise influence, as newly nuclear-capable allies would be less beholden to U.S. security dictates and more inclined to pursue policies that diverge—or even directly conflict—with American strategic objectives.

This fracturing of nuclear authority introduces a dangerous level of unpredictability into the international system. Historically, Washington’s control over extended deterrence has limited nuclear brinkmanship and crisis escalation—but a world populated by independent nuclear actors, each with their own security calculus, would be far more volatile. With more nuclear-armed states, the likelihood of intersecting crises that implicate U.S. interests and involve nuclear weapons outside of Washington’s control increases dramatically. In such an environment, the risk that states in Asia, the Middle East, Africa, or elsewhere might engage in nuclear coercion or outright use—without prior consultation or deference to U.S. strategic interests—becomes far more pronounced. Additionally, as former U.S.-umbrella states acquire nuclear capabilities, adversarial powers are likely to escalate their own nuclear strategies in response, setting off further waves of proliferation that destabilize entire regions and fuel conventional conflicts with nuclear dimensions. Simply put, as nuclear weapons proliferate, America’s freedom of action in the international system contracts, its ability to shape crises diminishes, and its influence weakens.

The dissolution of the nonproliferation era and the emergence of strategic entropy thus present a fundamental challenge to U.S. grand strategy. If Washington fails to reassert credibility in extended deterrence, it will face not only a diminished sphere of influence but also a nuclear order fragmented among multiple, increasingly unpredictable decision-making centers. What emerges is not just a multipolar world but a multipolar nuclear world, one where the privileges of American power—once reinforced by the ability to manage and contain nuclear risks—are diffused, diluted, and dangerously beyond Washington’s control.

References:

[1] “Russia Says It Won’t Discuss New Nuclear Treaty with US in Current Form,” Reuters, October 1, 2024, sec. World, Link.

[2] “DOD Releases 2023 Report on Military and Security Developments Involving the People’s Repu,” U.S. Department of Defense, accessed March 11, 2025, Link.

[3] “U.S. Extended Deterrence and Regional Nuclear Capabilities,” legislation, accessed March 11, 2025, Link.

[4] Ankit Panda, Vipin Narang, and Pranay Vaddi, “Nuclear Proliferation Will Haunt ‘America First,’” War on the Rocks, March 10, 2025, Link.

[5] Sylvie Corbet, “Macron Says He’ll Confer with Allies on Protecting Europe with French Nuclear Deterrence,” AP News, March 5, 2025, Link.

[6] Sylvie Corbet, “Macron to Discuss Nuclear Deterrence with European Allies. A Look at France’s Unique Strategy,” AP News, March 4, 2025, Link.

[7] Sylvie Corbet, “Macron Says He’ll Confer with Allies on Protecting Europe with French Nuclear Deterrence,” AP News, March 5, 2025, Link.

[8] Rudy Ruitenberg, “France Shares Intel with Ukraine as Macron Floats Nuclear Umbrella,” Defense News, March 6, 2025, Link.

[9] Sylvie Corbet, “Poland and Baltic Nations Welcome Macron’s Nuclear Deterrent Proposal,” AP News, March 6, 2025, Link.

[10] Sylvie Corbet, “Macron Says He’ll Confer with Allies on Protecting Europe with French Nuclear Deterrence,” AP News, March 5, 2025, Link.

[11] Ankit Panda, Vipin Narang, and Pranay Vaddi, “Nuclear Proliferation Will Haunt ‘America First,’” War on the Rocks, March 10, 2025, Link.

[12] Astrid Chevreuil and Doreen Horschig, “Can France and the United Kingdom Replace the U.S. Nuclear Umbrella?,” March 4, 2025, Link.

[13] Ankit Panda, Vipin Narang, and Pranay Vaddi, “Nuclear Proliferation Will Haunt ‘America First,’” War on the Rocks, March 10, 2025, Link.

[14] Gideon Rose, “Get Ready for the Next Nuclear Age,” Foreign Affairs, March 8, 2025, Link.

[15] Ankit Panda, Vipin Narang, and Pranay Vaddi, “Nuclear Proliferation Will Haunt ‘America First,’” War on the Rocks, March 10, 2025, Link.

[16] Ankit Panda, Vipin Narang, and Pranay Vaddi, “Nuclear Proliferation Will Haunt ‘America First,’” War on the Rocks, March 10, 2025, Link.