Europe: NATO, U.S. Retrenchment, and the Cost of Strategic Autonomy

Discussion surrounding a potential United States (U.S.) withdrawal from NATO has remained one of the defining debates since the beginning of Donald Trump’s second presidency. In recent months, particularly following the war involving the U.S. and Israel against Iran, tensions within the alliance have intensified, with President Trump openly criticising several European NATO allies and questioning their value to the alliance. As a result, the central question is no longer limited to whether Washington could formally leave NATO. Increasingly, attention should shift toward a more pressing issue: could Europe manage its security independently without substantial American support? What would be the strategic, military, and economic cost of such a shift, and would European states be capable of rebuilding or reorganising their defence capabilities quickly enough to confront emerging threats?

Importantly, despite the significant legal, political, and institutional constraints facing any U.S. president seeking to withdraw from NATO entirely, Washington could still adopt alternative approaches that stop short of formal withdrawal while substantially reducing its role within the alliance. Such measures could include lowering financial contributions, scaling back troop deployments across Europe, or withdrawing critical weapons systems and strategic capabilities currently provided by the U.S. In such a scenario, how vulnerable would Europe become, and how prepared would it be to fill the resulting gaps?

Europe’s priority remains continued support for Ukraine. From a macroeconomic standpoint, Europe could realistically replace the U.S.’ contribution. Since February 2022, U.S. military assistance to Ukraine has reached €64 billion, while Europe, including the United Kingdom, has provided €62 billion. In 2024 alone, U.S. military aid amounted to €20 billion out of a total of €42 billion. Replacing this contribution would require the EU to spend an additional 0.12% of its GDP, an amount that appears manageable. The more pressing issue is whether Europe could sustain such support without access to the U.S. military-industrial base.

A study by the International Institute for Strategic Studies (IISS) examined the costs Europe would face if the U.S. withdrew and European states sought to rebuild capabilities on a like-for-like basis. According to the study, replacing existing U.S. conventional capabilities alone would cost between $226 billion and $344 billion in new weapon systems and platforms. Addressing other military dependencies, including space, cyber, and nuclear capabilities, would push these costs even higher.

Although the costs of individual equipment items vary, the most expensive component would be the acquisition of 400 additional tactical combat aircraft, should European states invest in expanding their capabilities. This alone would account for just under 20% of the total estimated cost.

The cost of replacing 20 U.S. destroyers would account for just under 15% of the total estimated expenses. The third-largest cost category would be land-based long-range surface-to-air missile systems, estimated at $12.3 billion annually. Overall, when procurement and lifecycle costs over a 25-year period are taken into account, the total cost is estimated to reach approximately $1 trillion. The U.S. remains NATO’s largest military power and contributes around 62% of the alliance’s total defence spending. As a result, an American withdrawal would significantly weaken NATO. European states recognise that a NATO structure without the U.S. would face several challenges. Beyond the absence of American military coordination and strategic leadership, European countries have long been criticised for insufficient defence spending. In response, NATO members agreed in 2025 to increase defence expenditure to 5% of GDP by 2035. Yet even with higher spending, European countries collectively continue to lag behind the U.S. in overall military capabilities. The gap becomes even more apparent when European military spending is assessed on a country-by-country basis and compared with centralised military powers such as the U.S., Russia, or China.

One major challenge in the event of an American withdrawal would be the absence of a unified military command structure. Europe, including the United Kingdom, currently has around 1.47 million active-duty military personnel. However, the effectiveness of these forces is constrained by limited military integration and coordination. NATO’s command structure is built around the assumption that the Supreme Allied Commander Europe is an American general, a system that depends heavily on U.S. leadership and strategic support capabilities.

As a result, Europe faces two difficult options: either significantly expand troop numbers to compensate for the fragmented nature of national militaries, or rapidly strengthen military coordination and integration among European states. Without effective coordination, defence costs would rise substantially, while individual national efforts would likely remain insufficient to deter Russia. At the same time, any collective defence arrangement would still need to address issues related to burden sharing, moral hazard, and political coordination. European armed forces also suffer from high levels of military fragmentation. European countries collectively operate 178 different weapon systems, compared to only 30 in the U.S. The gap is equally visible in air power, where Europe fields 20 different types of fighter aircraft, while the U.S. relies on just six. The same pattern appears in main battle tanks, with European armies operating 14 different models compared to a single model used by Washington.

Anyways, it is also important to consider the potential costs for the U.S. in such a scenario. Washington could reduce spending by cutting its contribution to NATO and scaling back its military presence across Europe, Africa, and the Middle East. At the same time, the U.S. would lose access to a wide network of overseas military bases, limiting its ability to project power globally. This could force the U.S. Navy to operate closer to American shores, while long-range bomber operations would become more constrained due to reduced forward deployment capabilities.

More broadly, such a shift could accelerate the gradual retreat of the U.S. from its traditional role as a global leader, increasing the likelihood of a more inward-looking American foreign policy and a reduced commitment to international security frameworks.

Due to legal, logistical, political, and financial constraints, a complete U.S. withdrawal from NATO remains unlikely in the near term. The National Defense Reauthorization Act, signed into law in 2023 by former President Joe Biden, prevents any president from withdrawing from the alliance without either a two-thirds Senate vote or congressional approval.

However, Washington could pursue alternative approaches that stop short of formally leaving NATO while still reducing its role within the alliance. This could include lowering financial contributions, withdrawing certain weapons systems, or reducing troop deployments across Europe. The debate surrounding potential troop reductions in Germany reflects this possibility. Although such discussions may not always stem from a coherent strategic rationale and are at times linked to domestic political dynamics, they could still establish a precedent for future administrations seeking to scale back the U.S. military footprint in Europe.

Legal restrictions on troop withdrawals also exist, though loopholes and procedural pathways remain available. Under Section 1249 of the National Defense Authorisation Act for 2026, U.S. administrations face limitations on using Pentagon funds to significantly reduce troop numbers in Europe. The law prevents the Pentagon from lowering troop levels below 76,000 for more than 45 days unless several conditions are met. These include certifying that the reductions serve U.S. national security interests, consulting NATO allies beforehand, and submitting a detailed report to Congress.

While such measures make a large-scale withdrawal more difficult, they do not make it impossible. Even if politically controversial, financially costly, and logistically complex, a gradual reduction of the U.S. role in Europe remains a plausible scenario.

It is also important to note that this sentiment is not limited to Trump or even to the Republican Party. Several previous American presidents, including Dwight Eisenhower, Ronald Reagan, and Barack Obama, criticised Europe’s burden-sharing problem within NATO. However, Trump was arguably the first to treat the issue as a potential breaking point in transatlantic relations. His approach was notably pragmatic and transactional: if Europe failed to increase its contribution, the U.S. could gradually reduce its commitment.

During his presidency, Barack Obama repeatedly urged NATO allies to increase defence spending and reduce their reliance on American security guarantees. Following Russia’s annexation of Crimea in 2014, his administration pushed alliance members to commit to spending 2% of GDP on defence. This demonstrates that concerns over unequal burden sharing are not exclusive to Trump, but reflect a broader and increasingly bipartisan American perspective. As a result, similar debates are likely to continue under future U.S. administrations, regardless of party affiliation, particularly as Washington continues to shoulder a disproportionate share of NATO’s financial and military burden.

The implications of a reduced American role in Europe extend far beyond troop numbers or financial contributions. A major concern lies in the potential loss of access to critical U.S. military capabilities and weapons systems, especially at a time when some European security assessments warn of a possible Russian attack on another European state before 2028.

The debate surrounding the reduction of U.S. troops in Germany illustrates these tensions clearly. The decision has been viewed as particularly significant given Germany’s growing efforts to align with NATO expectations. Berlin has substantially increased defence spending and is expected to reach NATO’s 3.5% of GDP target by 2029. Germany is also among the largest providers of aid to Ukraine and has, for the first time since 1945, published a comprehensive national military strategy. The document was even praised by senior U.S. defence officials, including Elbridge Colby, the U.S. Under Secretary of Defense for Policy. Germany also demonstrated support for broader Western security priorities by preparing to deploy a minesweeper to the Strait of Hormuz following a potential U.S.-Iran ceasefire arrangement.

Despite this, tensions between Washington and Berlin have continued to surface, with some reports suggesting that Chancellor Friedrich Merz’s criticism of the Iran war, aimed largely at a domestic audience, may have contributed to friction with the Trump administration. This highlights how future American military commitments to Europe could increasingly become linked not only to defence spending levels, but also to broader political alignment with Washington’s strategic priorities.

As a result, one of the units reportedly likely to be withdrawn is a specialised U.S. force intended to deploy Tomahawk cruise missiles in Europe. Without such capabilities, Germany and its European allies could face a significant gap in long-range strike capacity, with no immediate replacement available. Berlin may attempt to address this gap through the development of an upgraded “Neo-Taurus” missile system. However, a substantial capability gap would still remain between the Taurus, as well as comparable European systems such as the Franco-British SCALP/Storm Shadow, and the U.S. Tomahawk missile. Although the Neo-Taurus is expected to extend operational range to around 1,000 kilometres, it is unlikely to become operational before 2030.

Such gaps would become particularly critical in the event of a Russian attack on a NATO member state in Europe. Current NATO military planning assumes that approximately 100,000 U.S. troops already stationed in Europe would be rapidly reinforced by up to 200,000 additional American troops, particularly armoured and mechanised units suited for Eastern European combat scenarios. Replacing this capability would require a major expansion of European military capacity equivalent to roughly 300,000 U.S. troops. In practical terms, this would likely require the creation of around 50 new European brigades, with a heavy focus on mechanised and armoured warfare capabilities.

Accordingly, the strategic risk of a reduced U.S. military presence in Europe lies not only in lower troop numbers, but also in the potential loss of advanced military capabilities that remain heavily concentrated in American hands. In many areas, European allies currently lack the industrial base, operational integration, or financial flexibility needed to replace these systems quickly. This could create serious vulnerabilities in deterrence, missile defence, intelligence gathering, and long-range strike operations.

Potential capability gaps could include the reduction or loss of systems such as Tomahawk cruise missiles and other long-range strike platforms, Patriot and THAAD missile defence batteries, advanced intelligence and surveillance assets including AWACS aircraft and Global Hawk drones, electronic warfare and cyber capabilities, as well as strategic airlift and aerial refuelling infrastructure essential for rapid NATO deployment and sustainment operations.

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