NATO summit 2025: Time to build a proper European pillar?

Neither an ‘EU-plus’ nor a ‘NATO-minus’ could fill all the gaps that would be left in European security if the US radically reduced its commitment to NATO. Europeans need a new forum to provide substitute defence guarantees and defence capabilities.

When NATO leaders meet for their summit in The Hague on June 24^th-25^th, they will have plenty to worry about: the war in Ukraine, Russian hybrid attacks, and where to find resources for higher defence spending. For most of them, however, the biggest worry will be the intentions of US President Donald Trump. When Trump attended the July 2018 NATO summit in Brussels, he had to be talked out of announcing that the US was leaving the alliance, according to his then national security adviser, John Bolton. What should Europeans do if he walks away from NATO this time?

What should Europeans do if Trump walks away from NATO at next month’s summit?

To begin with, they should not assume that he will not. In 2023, the US Congress passed legislation in an effort to stop a president taking such a step without its approval (ironically, co-sponsored by then Senator Marco Rubio, now Trump’s Secretary of State and National Security Adviser). Trump, however, has spent the last four months ignoring laws passed by Congress, while his administration’s actions and statements show that European security is no longer a priority for the US. The US ambassador to NATO, Matthew Whitaker, said on May 16^th that the US would start discussions later this year on reducing its forces in Europe. Even if the US remain formally part of NATO, it is almost certain that its military presence in Europe will be cut. European countries will therefore need to prepare to defend themselves with less or potentially no US help.

But how should Europeans strengthen their defence in the context of a (de facto if not de jure) US-less NATO? NATO officials and ministers have regularly warned that the EU cannot replace NATO and urged that the Union’s defence efforts should not compete with the alliance’s. But Trump has forced even traditionally pro-NATO politicians like German Chancellor Friedrich Merz to advocate “independence from the USA”. Without the US, however, neither the EU nor NATO would be well-equipped to defend Europe. There are at least three problems to solve:

• Coverage: which security guarantees for which countries?
• Command: who takes charge of military operations?
• Capability: what does the US provide, and how could its loss be mitigated?

Without the US, neither the EU nor NATO would be well-equipped to defend Europe.

Coverage
Deterrence relies on a potential adversary knowing that if it attacks one member of an alliance, the other members will pile in. On paper, Article 42.7 of the Treaty on European Union provides a stronger defence guarantee than NATO’s Article 5. The former states that if an EU member-state “is the victim of armed aggression on its territory, the other member-states shall have towards it an obligation of aid and assistance by all the means in their power”. The latter offers allies more flexibility: an ally only has to take “such action as it deems necessary, including the use of armed force”. 

The Article 42.7 guarantee on its own, however, is essentially meaningless, because the member-states allocate no forces to the EU and have no agreed plans to defend other member-states. The article more or less acknowledges its own shortcomings, when it states that for the 23 EU member-states that are also NATO allies, NATO “remains the foundation of their collective defence and the forum for its implementation”. The only occasion on which it was invoked was in response to terrorist attacks in Paris in November 2015.

The (near) certainty of a NATO response involving the US deterred any attack on Europe throughout the Cold War and afterwards. But what happens if one or more of the 23 EU and NATO members is attacked, and the US blocks consensus on a NATO response, or deems that no action on its part is necessary? What happens if one of the four non-NATO EU members is attacked? How, if at all, would EU member-states react if Article 42.7 were invoked in response to a full-scale military assault?  

On the other hand, seven European NATO members (Albania, Iceland, Montenegro, North Macedonia, Norway, Turkey and the UK) are not members of the EU. Turkey and the UK are among European NATO’s most significant military powers. If one or more of the seven were attacked, would the EU say “none of our business”? If NATO could not agree to respond to an attack on one of the 23 EU and NATO members, would the non-EU seven stay on the sidelines while EU member-states tried to mount a defence? It is hard to see how European security could be so easily divided up – but Ukraine’s fate shows what can happen to a country that lacks a reliable security guarantee, if an aggressive neighbour decides to risk attacking it.

Command
Even with such a guarantee, however, the second problem, command, would hamper Europe’s ability to fight off an attack if the US were not actively engaged. Despite the binding nature of Article 42.7, the EU has no command structure capable of running an operation to defend a member-state’s territory; and the NATO command structure relies heavily on American officers.

The Director General of the EU Military Staff, part of the European External Action Service (EEAS), is currently double-hatted as the head of the EU’s ‘operational headquarters’ (OHQ), the Military Planning and Conduct Capability (MPCC). The MPCC commands small non-combat missions outside the EU’s borders, such as the training missions in Somalia or Mozambique; as of this year, it is also supposed to become the operational headquarters for the EU’s 5,000 strong Rapid Deployment Capacity (RDC). The RDC is the EU’s latest effort to come up with an on-call fighting force, after the EU Battlegroups, first set up in 2005, which exercised regularly but were never used in a crisis. The MPCC has a permanent staff of 60, with an additional 94 ‘augmentees’ available in a crisis; but a study for the European Parliament suggested that even to provide command and control for the RDC would require a permanent MPCC staff of 250.    

For larger EU operations potentially involving the use of force, France, Germany, Greece, Italy and Spain each make available a national headquarters as an OHQ. The EU’s naval operation in the Red Sea and the western Indian Ocean, for example, is commanded from Rota in Spain. The operation commander (working in the OHQ) and the force commander (on the spot) for such operations are appointed by the EU’s Political and Security Committee on the recommendation of the EU Military Committee (a committee of senior military officers from the member-states). In other words, these are not permanent headquarters or appointments.

Alternatively, under the so-called ‘Berlin Plus’ arrangements agreed between the EU and NATO in 2003, the EU can make use of NATO planning capabilities, headquarters and enablers (such as communications). In that case, the operation commander is an officer from an EU member-state with a senior role in the NATO command structure. Before Brexit, this was the Deputy Supreme Allied Commander Europe, who is generally a British four-star general (or equivalent in the other services); since Brexit, the operation commander has been the Vice Chief of Staff at SHAPE (the headquarters of NATO’s Allied Command Operations), a French three-star general. But the Berlin Plus arrangements can only be triggered if there is consensus in NATO, which is why the only one of the EU’s current operations to benefit from NATO support through the Berlin Plus arrangements is Operation Althea, the EU peacekeeping operation in Bosnia and Herzegovina. The unresolved conflict between Turkey and Cyprus has been an obstacle in subsequent cases.

Unlike the EU, NATO has a large permanent command structure, with 6,800 personnel in SHAPE and other headquarters. There are three Joint Force Commands (JFCs) covering specific parts of the NATO area, and separate land, sea and air commands for the whole of the NATO area. The US has historically provided ten per cent or more of the staff in the NATO command structure, and is heavily represented at the most senior levels, with the Supreme Allied Commander Europe (SACEUR – NATO’s most senior military commander), two of the three JFC commanders and the land and air commanders.

Finding several hundred qualified staff officers to fill these American-held NATO jobs would be challenging for Europeans, particularly if they were doing it during a crisis, rather than as part of a planned drawdown of US forces in Europe. It would be better to start appointing ‘shadows’ now for key posts held by Americans, able to step in if necessary.

Agreeing on how to divide up the top jobs would be politically even trickier. An American SACEUR has provided not only a link to US command structures (he is double-hatted as the commander of US forces in Europe) but to the US nuclear deterrent. The Trump administration reportedly toyed with the idea of giving up the post of SACEUR to the Europeans before deciding against it. If Trump changed his mind again, a European SACEUR would have to come from one of Europe’s nuclear powers, the UK or France. But France does not take part in NATO’s nuclear planning (the one element of NATO’s integrated structure that France did not rejoin in 2009, because it wanted to reassure its population that the use of its nuclear deterrent would remain a matter for France alone); while the 23 EU member-states in NATO might feel that a UK SACEUR was not ‘European’ enough. It would be a big step for France to integrate its nuclear deterrent into NATO plans, as the UK does, and it might easily be reversed by a future French president.

Capabilities
Finally, there is the issue of capabilities. Europeans would have no problem, at least on paper, in providing enough personnel to defend their continent: NATO estimated that its European members had more than two million troops in mid-2024, compared with the US’s 1.3 million. Putin issued a decree in September 2024 to increase active-duty Russian personnel from 1.3 to 1.5 million.

The war in Ukraine has shown that mass still matters in war, even if on its own it may not be decisive. But troops also need enough weapons and munitions. It is extremely difficult to come up with a meaningful comparison between the quantities of useable military equipment in European inventories and that in Russia’s, particularly in the midst of a war in which Russia continues to suffer significant equipment losses every day. Some disparities are clear, however: according to a February 2025 policy brief from the Kiel Institute for the World Economy, Russia produced or refurbished 1,550 tanks in 2024 – more than the holdings of France, Germany, Italy and the UK combined. Russian production of artillery shells is around 3 million per year; Europe might produce 2 million this year if planned increases in production are achieved. Europe relies on the US Patriot missile system for long-range air defence, including against ballistic missiles of the kind Russia regularly uses against Ukraine. The US is responsible for supplying most of the multiple-launch rocket systems used by European countries, and the missiles for them. European NATO members have relied on the US coming to the rescue with more troops and materiel in a crisis.

Beyond the numbers of men and munitions available to each side, ‘C4ISR’ (command, control, communications, computers, intelligence, surveillance and reconnaissance) is also essential to success, and these are areas in which Europeans have relied heavily on the US. The US has enormous quantities of satellite and other reconnaissance assets, huge intelligence gathering and analytical capacity, secure communications and the ability to identify and target hostile forces quickly – all capabilities which have helped Ukraine to keep Russia at bay, according to The New York Times, and would be vital if other parts of Europe came under attack.

The EU is developing a satellite reconnaissance capability, but it is only scheduled to become operational sometime between 2028 and 2034. Until then, if the US withdrew intelligence support from European NATO allies, as it did from Ukraine in March 2025, Europe would have to rely on commercial satellites producing lower quality imagery. Europe is better equipped for navigation – the Galileo system is in some ways more accurate than the US GPS satellite navigation system. But when it comes to other forms of intelligence, neither the EU nor NATO have their own intelligence-gathering capability; both are limited to analysing whatever intelligence the member-states provide them with. There is no process for determining at European level what intelligence member-states should collect, so each intelligence service follows the priorities set nationally. In a crisis, the EU would be reliant on the intelligence its member-states were willing to share with each other, and on ‘the kindness of strangers’ from non-members. Without US input, NATO would also know much less about what adversaries and potential adversaries were doing.

As long ago as 2004, Michael O’Hanlon wrote in a CER report, ‘A European way of war’ that “sophisticated technology and new war-fighting concepts are important. But it is not necessary for Europe to mimic the US armed forces”. That remains true. Work on defence in the EU has focussed on capabilities, including replacing enablers such as C4ISR and heavy-lift transport aircraft provided by the US. But Europeans have not addressed systematically what they might do differently from Americans. To decide exactly what capabilities they would need, Europeans need to know who will fight, and how.

To decide exactly what capabilities they would need, Europeans need to know who will fight, and how.

Towards a European pillar 
Ironically, a partial answer to those questions used to be available in the form of the Western European Union (WEU), founded in 1948 but effectively superseded by NATO’s establishment in 1949. Article 42.7 took over the language of the WEU’s security guarantee almost verbatim, and in 2011 the WEU dissolved itself. Despite the hopes of some in the UK, there was no revival of the WEU after Brexit. But prior to 2011, the WEU gave all European states that were either members of the EU, NATO or both a voice in discussions on European defence, even if its practical role was very limited. The WEU’s full members were the states that were members of both the EU and NATO; countries that were members of the EU but not NATO (plus Denmark, which had an opt-out from the EU’s Common Security and Defence Policy until 2022) were observers, and countries that were members of NATO but not the EU were associate members.

NATO has been talking since at least the late 1980s about strengthening its European pillar; but it has struggled to agree what that should mean. For some countries, especially France, the pillar is a European defence effort that complements NATO (among other things, “increasing EU visibility within NATO”, according to Thierry Tardy in a January 2025 article); for others, it signifies the collective contribution of European members of NATO, whether or not they belong to the EU.

The European pillar cannot just be an EU caucus in NATO: it cannot ignore the contribution that countries like Norway, Turkey and the UK can make to the defence of Europe. Equally, the European pillar cannot exist completely independently of the EU, when the latter is trying to ensure that the European defence industrial base can produce what Europe needs to defend itself, in the quantities that it needs and at a price that it can afford.

Russia’s attack on Ukraine and Trump’s reluctance to defend US allies should drive those European countries that want to, and are members or candidates to become members of NATO, the EU or both, to set up an inclusive forum for defence. Such a forum should be institutionally linked, as the WEU was, to both the EU and NATO, but should be less of a talking shop and more of a decision-making body. A proper European pillar would provide a binding defence guarantee covering all its members, not subject to a US veto; a link to NATO’s command structure, Europeanised as necessary, to enable it to conduct operations; and a link to the EU’s defence industrial policy tools, enlarged to allow other European countries to benefit from them, to foster a pan-European defence industry able to produce weapons and munitions at scale. Whatever Trump says or does at the NATO summit in The Hague, Europeans should come out of the meeting having taken the first steps to agree the design of a European pillar and to start building it.

Ian Bond is deputy director of the Centre for European Reform.