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NATO summits usually offer more spectacle than substance. Not this time. As Secretary General Mark Rutte cracked about U.S. President Donald ������Ƶ jabs at Iran and Israel at June’s Hague summit, NATO members were quietly agreeing to something extraordinary: the largest peacetime military commitment since the alliance’s founding. Each country committed to spending five percent of its GDP on defense by 2035, more than double the current levels. Rutte’s goal was clear: Keep the United States engaged, tradeoffs be damned. The agreement opens a new chapter in the alliance’s 80-year history, one that is ambitious, expensive, and chock-full of fine print.

The spending shift could fundamentally restructure European economies, potentially creating a more autonomous European defense industry that depends less on American suppliers. Yet beneath the summit’s mutual backslapping, the pledge has already begun exposing deep fractures within the alliance. Spain negotiated an opt-out before the ink was dry. Slovakia’s leader called the targets "” And predictably, those allies farthest from Russia—and thus its threat—tend to be the most resistant to paying, leaving Eastern European nations to carry the burden of preparing for Russian aggression.

Russia’s full-scale invasion of Ukraine in February 2022 marked the of NATO, which in some quarters had appeared to outlive its founding Cold War mission. As Ukraine rounds the corner to a fourth year of war, the persistent threat of Russia’s expansionist ambitions continues to invigorate the alliance, helping birth “a new NATO,” of Alexander Stubb, the President of Finland. Russia’s neighbor became NATO’s 31st member state in April 2023, trading decades of nonalignment for the promise of collective security.

Unlike its previous incarnation, this reborn NATO is defined by unprecedented spending commitments. The five percent GDP target appeared to be the hard pill the allies chose to swallow that President Trump stays committed to the alliance in general and to upholding Article 5 in particular. In effect, Europe accepted a transactional bargain: unprecedented defense expenditures in exchange for continued American security guarantees.

But despite the uplifting atmosphere following the summit, marked by Rutte’s sycophantic to Trump and the U.S. president’s sudden realization that NATO was, indeed, ",” the commitments to raise defense spending over the next decade are now sowing disagreements among EU members. With some European states lacking the willingness to pay and others lacking the luxury of waiting until 2035 for the defense sector to recover after years of underinvestment, the pledge to raise defense spending to five percent of GDP will likely test not only transatlantic relations but the very unity of the European Union.

Few believe that European allies would have accepted such a sharp increase in defense spending if not for the to retain U.S. support for NATO. Throughout his presidency and campaign, Trump repeatedly questioned the value of the alliance and made clear that the U.S. commitment to Article 5, the mutual defense clause at NATO’s core, was not unconditional. In his view, allies that failed to spend enough on their own defense could not rely on American protection.

Of course, Trump is not the first—or likely the last—American president to complain about lopsided burden-sharing commitments. U.S. officials have voiced frustration for decades over European allies’ failure to meet agreed-upon spending benchmarks. What sets Trump apart is his openly transactional approach to security guarantees. Unlike his predecessors, who treated NATO as a strategic pillar of American foreign policy, Trump has framed it as a deal that must deliver measurable returns to be worth keeping.

Like it or not, ������Ƶ approach—however awkward and unorthodox—seems to have spurred a shift in European defense strategy. In March 2025, the European Commission the White Paper for European Defense alongside the ReArm Europe Plan, signaling a shift toward a more autonomous and proactive security strategy. The documents call for immediate, large-scale increases in defense spending at both the national and EU levels to build up Europe’s own defense industry and create a common market for military equipment. As Commission President Ursula von der Leyen put it, the goal is to “” and reduce reliance on non-EU suppliers.

The EU thus aims to develop, produce, and procure most of its defense technology locally, reducing its dependence on the U.S. defense market. But this push for strategic autonomy demands a sharp and sustained increase in defense spending over the next decade—a prospect that many EU states find unwelcome, albeit for different reasons. The ambitious targets have already drawn pushback from allies who question both their necessity and their feasibility.

Even before the NATO summit concluded, Spain challenged the unanimity of its vision by to be exempt from the allies’ spending target. The country has emerged as a vocal skeptic of the pledge. Unlike Eastern European or Nordic countries, Madrid does not view Russia as an immediate military threat. As Prime Minister Pedro Sánchez noted earlier this year, there is no risk of “Russia bringing its troops across the Pyrenees.” Instead, Spain has prioritized economic recovery and fiscal stability. With 3.2 percent GDP growth in 2024—one of the fastest in the eurozone—the Sánchez government has made that momentum central to its political narrative.

Spain currently allocates only about of its GDP to defense, or roughly 20 billion euros, the lowest rate in the alliance. Meeting the five percent target would require nearly 80 billion annually. Even the government’s more modest pledge to reach 2.1 percent by 2035 would mean almost doubling current spending, adding at least 16 billion euros a year. That kind of increase would be hard to sustain without sacrificing investments in welfare, infrastructure, or climate policy. Spain’s exemption may be fiscally sound at home, but it exposes a broader truth: NATO’s unity may be politically declared, but it is economically uneven.

Since a single NATO member’s veto could block the entire summit resolution, Spain managed to negotiate an opt-out for itself, allowing it to avoid committing to the five percent target spending. However, NATO Secretary-General Mark Rutte, who that “NATO has no opt-outs, and NATO does no side deals,” has yet to agree with Spain on an alternative investment strategy. This standoff reveals a critical vulnerability in NATO’s consensus-based decision-making: Any member willing to break ranks can hold the alliance’s unity hostage.

Spain’s attempts to avoid sharing the burden of European rearmament with fellow EU states and NATO allies sparked responses that highlight the tensions and vulnerabilities of both the EU and NATO’s vision for moving forward in unity. Various representatives of European nations anger and disgust, finding that Spain’s determination to avoid sacrifices in the name of shared European security was unfair and set a “bad example.”

Spain found a in Robert Fico, the populist leader of Slovakia, the only NATO state that could contest Spain’s degree of underinvestment in defense. Known for his stance against military aid to Ukraine, EU sanctions on Russia, and Ukraine’s potential NATO membership, Prime Minister Fico has already the idea that Slovakia would be better off trading its NATO allies for “neutrality” and characterized the NATO defense spending goals as “absolutely absurd.” It is safe to assume that Slovakia will likely follow Spain’s “bad example” of military underinvestment rather than NATO and the EU’s vision of a drastic increase in spending for European rearmament.

Though Spain and Slovakia’s objections to the NATO summit’s breakthrough resolution attracted from states like Sweden, Poland, and Denmark, they are not alone in seeking to be exempt from building a more “” at the price of tax increases, growing debt, and weakened social programs. Canada and Belgium their intention to seek maximum flexibility in defining defense spending targets. Meanwhile, Trump, the primary architect behind the five percent spending goal, that the United States, which has been “supporting NATO so long,” has neither the intention nor the obligation to meet the NATO spending target.

With the United States, Canada, Belgium, Spain, and Slovakia stepping back from NATO’s five percent pledge, 27 members remain. History offers little reason to believe they will all follow through. In 2014, NATO allies committed to spending two percent of GDP on defense. By 2021, only six had done so. Russia’s full-scale invasion of Ukraine in 2022 finally pushed most of the alliance to comply. As of this year, 23 of NATO’s 32 members meet the two percent threshold. If it took a war to reach that goal, what kind of crisis would be needed to hit five percent?

A new geography of fear helps explain who is willing to spend. Countries that share borders with Russia or have lived under its shadow tend to allocate the most to defense. For them, the threat is immediate. Estonia, Latvia, and Poland all spend more than three percent of GDP. Lithuania, with fewer than three million citizens, plans to spend between five and six percent by 2026. Polish Defense Minister Władysław Kosiniak-Kamysz has his country a “model member,” not because of what it says, but because of what it spends.

This fear-driven logic creates a growing split within the alliance. For states on NATO’s eastern edge, defense spending is not a debate. It is a necessity. Others, especially in Southern and Western Europe, do not see the same urgency. While the United States and its eastern allies have pressed for the five percent goal to be met by 2030, countries such as Italy and Spain have asked for a deadline of 2035. On paper, the five-year difference may appear minor. In reality, it signals a deeper fault line with real implications for NATO’s strategy in dealing with Russia.

Allies facing the threat head-on want forward deployments, hardened infrastructure, and robust deterrence measures now. Others prefer a slower ramp-up, prioritizing diplomatic engagement, domestic constraints, and industrial ramping over immediate troop readiness. This divergence affects everything from procurement timelines to the placement of new battle groups, and it raises a critical question: How can NATO deter an adversary if its members are not aligned on the nature or urgency of the threat?

NATO can only deter effectively if its members converge not just on spending targets but on shared priorities, timelines, and threat perceptions. Right now, that convergence remains elusive. For frontline states, deterrence means visible military readiness and rapid reinforcement. For others, it means political solidarity and economic resilience. Until the alliance resolves this strategic dissonance, defense spending risks becoming more of a performative benchmark than a functional tool of deterrence.

Unity, it turns out, is not a line item. It is a mindset—and one that can’t be declared into existence. Whether NATO can forge it in time may define the next chapter in Europe’s security order.