US threat to withdraw from NATO sparks debate on EU enlargement to secure the continent

Brussels – Security, economics, geopolitics, NATO, the rule of law and shared values. EU enlargement has never been so exposed to competing forces pulling it in different directions, often beyond the direct control or political will of the current EU member states.

As widely expected, the return of US President Donald Trump to power has had a profound impact on this agenda – from Ukraine to the United Kingdom, from the Western Balkans to the Nordic countries, and even, to a certain extent, Canada. The issue is now further complicated by the prospect of a weakened NATO, following US threats to withdraw from the Alliance, and the resulting scenario in which the EU may be compelled to assume far greater responsibility for European defence and security.

This is what the Ukrainian president, Volodymyr Zelensky, recently suggested during an interview on the UK’s leading political podcast The Rest Is Politics. Discussing a scenario in which the US were to withdraw from NATO, he urged the EU to evolve beyond “its current form” and to include “more countries,” namely Ukraine, Türkiye, the UK and Norway. “These are four strong countries which are part of Europe,” he said, stressing that their combined armed forces are “stronger” than Russia’s.

Zelensky’s argument centres on the need to match Russia’s military capacity – something Europe cannot achieve, particularly “without Ukraine and Türkiye.” According to the latest data published by the International Institute for Strategic Studies (IISS), Russia’s armed forces number approximately 1,264,000 active personnel. This is broadly comparable to the combined forces of Ukraine (677,000), Türkiye (355,000), the United Kingdom (150,000) and Norway (24,000). While EU–NATO members together can rely on around 1.286 million active personnel, they fall short when it comes to reserve forces: roughly 942,850 compared with more than double that figure for Russia.

This is why the Ukrainian president called for a shift in the focus of EU enlargement. “Security comes first, economy second. Not vice versa.” In his view, expanding the European Union to include Ukraine – a non-NATO member and EU candidate – alongside the three European NATO members – the UK (a former EU member), Türkiye and Norway (both with frozen applications) – would help ensure “control of the seas, secure skies and the largest land forces.” All this comes against the backdrop of Moscow’s plans to expand its armed forces to 2.5 million personnel by 2030. “It is not about offence,” Zelensky stressed, but about the need for Europe to “think about security and how to preserve its independence.”

European security without NATO?

“We still do not know how realistic a full US withdrawal from NATO is, but it remains unlikely,” cautions Giuseppe Spatafora, Research Analyst at the European Union Institute for Security Studies (EUISS), reached by The New Union Post. The extent of any US disengagement is of paramount importance, because “it will determine both the areas in which Europe would need to act on its own and the degree of urgency.”

While countries such as Ukraine and Türkiye “can provide certain assets” – including large armed forces and experience in modern warfare – Spatafora warns that “they cannot fully replace the US security umbrella” within NATO. Not to forget the institutional constraints. Even in the absence of the United States, the North Atlantic Treaty Organization would likely remain the central framework for Europe’s defence, given that “it has the necessary structures in place and a broader membership,” including all the European countries mentioned by Zelensky, with the exception of Ukraine itself.

In such a scenario, however crucial the issue of defence may become, EU enlargement is unlikely to abandon its value-based nature in favour of a more security-driven approach. The EUISS research analyst argues that attention should instead focus on ad hoc coalitions, as the EU “can play a role in the defence industrial dimension of the equation.” While close cooperation with Ukraine’s industrial base is already under way, engagement with Türkiye will remain limited “as long as long-standing disputes endure” with certain EU Member States, notably Greece and Cyprus.

In other words, while “more ad hoc and sector-specific cooperation, perhaps behind closed doors,” is foreseeable – particularly in the event of a partial US disengagement from NATO – even analysts covering European security issues doubt that “any fast-track accession process will get under way.” The discussion, Spatafora notes, goes beyond the European Union as such, as “its role in defence, while growing, is still limited to the defence industrial market.” Space for countries such as Ukraine and Türkiye could instead be carved out through “flexible formats,” allowing them to contribute in ways that help offset any potential shortfall in US firepower – “both literal and metaphorical.”