For over seventy years, U.S. military power has formed the backbone of Europe’s security architecture. American leadership enabled the continent to prioritize political integration and economic development while relying on a trans-Atlantic alliance to deter external threats. That arrangement is now under increasing strain. In his second term, President Donald Trump has pushed European allies to commit up to 5 percent of their gross domestic product to defense and has signaled that the United States may no longer provide a conventional military backstop on the continent.
Some suggest that this is a calculated effort to compel Europe to assume greater responsibility and that the United States will remain committed to the alliance. Yet even if that is the intent rather than absolute abandonment, the effect is the same: Europe would be prudent to plan for a future without an American security guarantee.
What follows from such a shift is far from predetermined. One possibility is that the shock of American disengagement catalyzes greater European unity and strategic coherence. Another is that the loss of U.S. leadership accelerates internal divisions and geopolitical vulnerability. Which path Europe takes will depend on choices made now — by policymakers who should prepare for contingency, not continuity.
Europe Left Alone Yet More United
In the first scenario, European NATO member states respond to a sustained American withdrawal by expanding their security capacities through a range of measures, including the formation of new partnerships, the enlargement of their armed forces, and the strengthening of domestic defense industries. Unlike more ambiguous past episodes, Washington is now making its intentions clear through concrete actions — systematically withdrawing from Europe and signaling that it no longer considers the continent a strategic priority by either de jure or de facto dismissal of security agreements. In an effort to concentrate on countering China and driving a wedge between Beijing and Moscow, Washington either intensifies cooperation with Moscow or begins clearly recognizing a Russian sphere of influence in its immediate neighborhood. These moves send a message that the U.S.-European alliance is no longer a U.S. priority, and the United States is not likely to be positioned to come to Europe’s defense in the event of Russian aggression — or be willing to do so.
European leaders come to recognize that their only viable path forward lies in developing a more unified and strategically coherent security architecture. In the absence of U.S. leadership, previously peripheral actors become more central. The United Kingdom, despite no longer being part of the European Union, takes an important role by mobilizing support from Commonwealth countries such as Canada and Australia to contribute to European security initiatives. At the same time, the United Kingdom maintains close ties with the United States and increasingly acts as a bridge between the two sides of the Atlantic.
France leads the initiative to reshape Europe’s defense posture, with Germany — initially cautious — joining as the urgency of the situation becomes clear. Over time, countries like Norway, already closely aligned with the European Union, move toward full membership, further consolidating the European defense framework. The European Security Council evolves into a more robust and active institution, increasingly taking on strategic coordination responsibilities.
To compensate for the loss of the U.S. nuclear umbrella, France and the United Kingdom jointly develop a European nuclear deterrent framework, offering protection to E.U. and partner states in the new security environment.
Although Europe’s overall military capacity remains limited, a significant degree of deterrence is achieved through intensified cooperation and an unprecedented level of political unity. Major defense capabilities are developed and strategically positioned, with a particular focus on bolstering troop presence and military infrastructure in the Baltic states and Eastern Europe to deter potential Russian aggression.
As confidence in NATO declines, several European countries reduce their contributions to the alliance and begin to question its relevance altogether. Some even consider formally withdrawing or adopting a more passive role, viewing continued alignment with the United States as a constraint on foreign policy — particularly in relation to China. Over time, Western European states begin reassessing their broader strategic priorities, seeking to balance multiple global challenges, while Eastern European countries continue to view Russia as the principal and immediate threat.
Despite occasional disagreements from states such as Hungary and Slovakia, Europe manages to maintain a degree of cohesion. This growing unity fosters the emergence of a distinct European identity in international affairs, defined by the capacity to pursue independent strategic objectives. As a result, Europe increasingly positions itself as a global power, balancing between the United States and China, while also independently cultivating partnerships with emerging actors such as India and various Central Asian states.
The End of European Multilateralism
This scenario builds on the core premise that Europe’s transformation from a continent of conflict to a liberal success story was made possible in large part by long-standing U.S. security guarantees.
As in the previous scenarios, the initial response to a U.S. withdrawal is a concerted European effort to increase defense capacity. The United Kingdom becomes more deeply engaged in continental security and shares a leadership role with France, while Germany accelerates its rearmament and begins to close the capability gap. In the early phase, this cooperative momentum holds. Faced with the shared urgency of deterring immediate threats, particularly from Russia, European states coordinate military investments, intelligence sharing, and regional force deployments with relatively little friction.
Over time, however, as national capacities grow and the immediate sense of unity fades, underlying tensions begin to resurface. France — long invested in shaping Europe’s strategic direction — grows uneasy about the prominent role of the United Kingdom, a non-E.U. member, in continental security affairs. The United Kingdom, for its part, remains committed to a strong presence in Europe and shows little interest in deferring to E.U. leadership. Rising militarization, combined with the ascent of right-wing political forces across the continent, brings renewed focus to questions of national status, strategic autonomy, and geopolitical influence.
Germany, having rapidly expanded its defense capabilities, begins to assert that its growing role warrants greater strategic influence — particularly in decisions traditionally shaped by Franco-British leadership. The inclusive and consensus-driven model of European multilateralism begins to erode, giving way to new patterns of fragmentation, rivalry, and regional alignment.
In this increasingly competitive environment, European states begin prioritizing bilateral, interest-driven partnerships — both among themselves and with external actors. With multilateral institutions losing coherence, states pursue transactional arrangements tailored to their own security and strategic needs. Confronted with prolonged uncertainty and lacking a credible collective deterrent, some Eastern European countries — particularly those geographically vulnerable or politically divided — may even adopt a bandwagoning approach by seeking limited accommodation with Russia. Meanwhile, other states on the periphery, such as Poland, the Baltic countries, or Finland, strengthen bilateral defense ties with like-minded partners in an effort to resist Russian influence as much as possible.
Rising uncertainty and deepening divisions bring long-suppressed historical tensions back to the surface, particularly territorial disputes and ethnic grievances. In the Balkans, the unresolved Kosovar–Serbian issue reignites, with Russia openly supporting Serbian claims and emboldening nationalist elements. Across Central and Eastern Europe, the resurgence of nationalism prompts Hungary to pursue a more assertive policy aimed at “protecting Hungarian-speaking populations” in Romania, Slovakia, and Serbia, fueling regional friction. Russia intensifies its hybrid operations across the Baltics, the Balkans, and Moldova, justifying its actions by invoking the need to defend “Russian-speaking minorities” in these areas. Meanwhile, in the Eastern Mediterranean, the absence of a robust deterrent framework encourages Turkey to escalate its involvement in Cyprus, raising the risk of a direct confrontation with Greece.
What Europe Needs to Do to Achieve Unity and Avoid Fragmentation
Whether Europe moves toward strategic unity or drifts into fragmentation will depend not only on the trajectory of U.S. disengagement, but also on Europe’s ability to confront internal divisions and respond pragmatically to a more fluid global order. While the United States has not fully withdrawn from Europe, its long-term commitment appears increasingly uncertain. The challenge for Europe is not to replace U.S. leadership outright, but to build the resilience and internal coordination needed to manage growing security responsibilities amid shifting global alignments.
Strategic autonomy, even in a limited form, will likely face considerable headwinds. Europe is internally divided by geography, threat perception, and political will — and also constrained by structural factors. Defense spending remains uneven, energy dependence is unresolved, and aging populations place pressure on budgets and manpower alike. The capacity to project power independently — especially in nuclear terms — remains far below that of the United States or Russia.
In light of these realities, near-term efforts may center more on practical coordination. Joint procurement in key areas such as missile defense, cyber capabilities, and logistics may offer more immediate gains. Enhanced interoperability among command structures, particularly across eastern and western members, could reduce duplication and build trust incrementally. A loose leadership framework — anchored in France, Germany, and the United Kingdom — may serve as a useful starting point, especially if it includes participation from Poland, Italy, and the Nordics.
Externally, Europe will likely continue to hedge. Deeper partnerships with Japan, Australia, ASEAN, and others could help reduce exposure to overdependence on any one actor, particularly China. The relationship with Turkey will remain complicated, yet strategically indispensable, especially given its position as a NATO ally and its independent regional posture.
The path toward autonomy will not be quick or comprehensive. It will be shaped less by quick solutions than by incremental adaptation, flexible coalitions, and shared burdens where feasible. Europe’s ability to coordinate within these constraints may determine not only the future of its unity — but its relevance in a world of dispersed power and conditional alignments.
Ali Mammadov is a Ph.D. researcher at George Mason University’s Schar School of Policy and Government and the managing editor of the Center for Security Policy Studies. His work focuses on military alliances, great power competition, and the role of rising powers in global security.
Image: Number 10 via Wikimedia Commons
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