Europe faces a collective action problem. There is growing recognition in Europe that the Euro-Atlantic community is confronted with an existential security threat from Russia – one which may last a generation or more and which could result in armed conflict against an EU member state within three to five years.[1] At the same time, Europeans are faced with the stark realisation that they can no longer rely on the United States to provide the essential military capabilities to ensure their collective defence. Europeans are thus confronted with the challenge of reforging an effective and credible European deterrence capability. Beyond that, they need to collectively craft a European grand strategy that integrates all instruments of power into a coherent strategy for navigating the turbulent waters of an increasingly unpredictable multipolar global order.
This should not be an insurmountable challenge. Yes, Russia – with a GDP equivalent to that of Italy – spends more than European NATO on its armed forces[1], and produced more ammunition than all NATO countries collectively in 2024. The Russian army has also grown since the invasion of Ukraine and become more adept at waging war with new technologies and tactics. Russia’s economy is now geared up for war and Putin plans to enlarge the armed forces further to 1.5million personnel. But on the other hand, Europe has a collective GDP that is 12 times larger than that of Russia, and five times its population.[2] As the EU defence commissioner Andrius Kubilius has noted, ‘450 million Europeans should not have to depend on 340 million Americans to defend themselves against 140 million Russians who can’t defeat 38 million Ukrainians.’[3]
An effective European deterrence requires both capabilities and resolve. Creating the requisite capabilities will take between 5-10 years, but rearmament has begun, and the necessary investments are now being made. The period of greatest danger is between 3-8 years – after Russia has reconstituted and redeployed its offensive military capabilities, and before European rearmament generates sufficient defensive capabilities and strategic enablers to create a deterrent effect.
Generating the necessary military capabilities is a necessary but not sufficient condition for effective deterrence; the other is forging sufficient political will and cohesion to demonstrate resolve, and to drive the formulation and implement of a new European grand strategy. This is where Europe’s collection action problem becomes acute: which actors will drive the process of forging political cohesion and resolve, and in which institutional fora?
The argument made here is that this process will not emerge within the EU or NATO; rather, it will be driven in the first instance from below, from ‘plurilateral’[4] groupings of like-minded states that can generate the necessary military capabilities and demonstrate resolve in shaping a strategy to support Ukraine and deter Russia. More specifically, it will come from two sources: political-security strategy will emerge from diplomatic gatherings of like-minded states (‘coalitions of the willing’); effective defence cooperation will come from ‘plurilateral’ forms of functional military and political cooperation, often operating on a regional basis. These more flexible and pragmatic forms of cooperation between like-minded countries can provide the building-blocks for shaping a broader European consensus within the EU and forging a stronger European pillar of NATO. But the impetus for this will have to come from below and from outside these organisations, rather than from a top-down process of collective deliberation and consensual policy formulation.
Europe consists of a diverse range of small, medium and large states, with different geostrategic interests, different capabilities and strategic cultures, different histories, cultures and political values. Most are members of both the EU and NATO, but the memberships of these two organisations do not overlap completely, and there are some obvious discrepancies: the EU has 27 members but does not include the UK or Norway, and includes problematic countries like Hungary and Slovakia, as well as free riders like Ireland and Austria. NATO’s 32 members include Canada and Turkey, along with the ‘elephant in the room’ – the United States, which has its own geostrategic priorities and domestic political idiosyncrasies. Together, the EU and NATO constitute the twin pillars and institutional foundations of Europe’s security architecture, and close cooperation between them is the key to Europe’s security. Both therefore have an essential role to play in reforging European deterrence.
However, both are large organisations with diverse memberships, and both suffer from ‘institutional friction’[5], making their decision-making processes slow, cumbersome and ponderous. Decisions often reflect the lowest common denominator principle, and consensus-building tends to result in sub-optimal outcomes. In his 1867 study of the British Constitution, Sir Walter Bagehot distinguished between its ‘dignified’ and ‘efficient’ parts. He argued that the theory of a constitutional monarchy with parliamentary supremacy masked the real reality of cabinet government. The ‘dignified’ parts, he argued, ‘excite and preserve the reverence of the population’, whereas the ‘efficient’ parts are ‘those by which it, in fact, works and rules’. The two parts, he argued, were complementary and functional in respect to the whole. The Euro-Atlantic security system also has its dignified and efficient parts: the EU and NATO constitute its ‘dignified’ parts, but plurilateralism and coalitions of the willing are its ‘efficient’ elements.
This can also be analysed in terms of ‘social network theory’ which is a science which studies the formation, evolution, structure and effects of networked interactions between actors (with interactions being termed ‘edges’ and actors ‘nodes’).[6] Network theory has two different models for explaining the emergence of network clusters: ‘homophily’, which suggests that networks are easier to form and more resilient between actors who share similar attributes (as suggested by the proverb ‘birds of a feather flock together’); and the ‘preferential attachment’ model, which suggests that networks will form among ‘heterophilic’ members who share fewer attributes, but who are influential actors that are attractive partners because of their capabilities and because they already have a range of interactions with other states. Heterophilic networks require a greater investment in time and energy to establish effective communication and their interactions tend to be looser and weaker, but they can complement homophilic networks by linking in with broader clusters of networks.
One network cluster characterised by ‘preferential attachment’ is the ‘European Group of five’ (E5) which was initiated by German Defence Minister Boris Pistorius, and which brings together Europe’s top five defence spenders (Germany, France, the UK, Poland and Italy).[7] Faced with the prospect of Trump’s re-election, the E5 first met in Berlin on 25 November 2025 to hammer out a joint position on support for Ukraine and a strategy for ‘keeping the transatlantic bond strong, while at the same time significantly increasing the European contribution to deterrence and defence’. Subsequent meetings of the E5 were held in Paris in January 2025, Brussels in February 2025 and Paris on 12 March 2025.[8] These meetings have also been attended or briefed by the NATO Secretary-General, European Commission President, the European High Representative and the European Commissioner for Defence, thus linking this core grouping with twin pillars of the Euro-Atlantic community.
With the shock of the Munich Security Conference and the Trump administration’s ‘peace plan’, a broader diplomatic ‘coalition of the willing’ has formed around the core of E5. The lead has been taken by British Prime Minister Starmer and French President Macron, who have demonstrated a welcome ability to provide joint leadership to a broader grouping of European countries willing and able to support Ukraine and strengthen European security and defence cooperation. Summits have been held in Paris and London which have brought together the E5 along with a shifting constellation of other like-minded states, including the Nordic four, the Netherlands, Czech Republic, Romania, Spain, Turkey and Canada. These summits have also been attended by the NATO Secretary-General and presidents of the European Council and Commission. With the uncertainties generated by American diplomacy, various constellations of European allies have been meeting regularly to hammer out a joint response on Ukraine and the future of European security.
The flurry of plurilateral diplomatic meetings that have taken place over recent months represent one element of the ‘efficient’ (to use Bagehot’s term) functioning of consensus-building and strategic planning in Europe. Given the ‘institutional friction’ of larger and more formalised multilateral organisations like the EU and NATO, plurilateral agreements between groups of like-minded states represent a way of building consensus and generating collective action. They require less horse-trading and compromises than multilateral agreements and can create a ‘gold standard’ for broader multilateral agreements at a future date. They can also facilitate the more drawn-out process of interest articulation and integration with the EU and NATO by creating building-blocks of consensus and compromise, around which others can cluster.
The other ‘efficient’ element of European security and defence cooperation is what Brendan Flynn has termed ‘interstitial institutionalism’.[9] These are ‘small, military co-operative institutions that exist at the interstices between the national level and multilateral institutions, foremost NATO and the EU’. Such forms of interstitial cooperation have proliferated over the last ten to fifteen years, often between ‘homophilic’ groups of neighbouring states sharing similar attributes such as regional interests and strategic culture. They emerge to fill the spaces between NATO and the EU, and ‘provide contingency in the guise of institutional ‘work-arounds’ to deal with both the limits of national defence provision and the complexities of getting agreement within what are now a very large NATO and EU’. They therefore hit the sweet spot between ad hoc ‘coalitions of the willing’ and multilateral security institutions, offering economies of scale and providing greater flexibility and ability to respond quickly and effectively.
The emergence of a plethora of interstitial forms of defence and security cooperation has created veritable ‘alphabet soup’ of acronyms for minilateral defence cooperation resulting in an ‘archipelago of defence cooperation’ across Europe. The concern has been that these islands of cooperation constitute a fragmentation and dissipation of European defence efforts along sub-regional and geopolitical lines, and there has been discussion of how to stitch together these bi- and minilateral groupings so that the whole is more than the sum of their parts.[10] In this regard, the Nordic-Baltic region offers a prime example of how these islands of defence cooperation can be woven together generating synergies that strengthen European deterrence and signal collective European resolve.
The Nordic-Baltic region is now the frontline of the Euro-Atlantic community and the region of closest geostrategic proximity to Russia. It has also witnessed a proliferation in forms of interstitial cooperation over the last decade or so. What is also increasingly apparent is that the multiple forms of defence and security cooperation are now interlocking and overlapping in ways that generate both new synergies and demonstrate collective political cohesion. The key to unlocking this potential for synergies has been Sweden and Finland’s membership of NATO, which has made it possible to view the wider North Atlantic-Nordic-Baltic-Arctic region as one theatre of operations. It has also removed obstacles to closer cooperation across the region. The new tapestry of defence cooperation in the wider region consists of several distinct network clusters and plurilateral groupings, which also intersect and interlock with broader military-political structures in the Euro-Atlantic community.
At the core of this are multiple forms of bilateral defence cooperation, of which Swedish-Finnish defence cooperation is one pertinent example: this is manifested in FISE Naval cooperation as well as Cross Border Training between air forces, and more recently, Sweden’s decision to take the lead in establishing a FLF[2] in Finland from 2026 onwards. Sweden and Finland also cooperate trilaterally with Norway in regular aerial training and exercises, and share similar approaches to ‘total defence’. These dyadic and triadic networks of cooperation are anchored in NORDEFCO and the Nordic Council. Nordic security and defence cooperation is also now linked to the cluster of bi- and tri-lateral defence cooperation in the Baltic states through Danish and Swedish participation in the FLF in Latvia, as well as the NB8 forum[11], the importance of which has grown considerably over recent years. The NB8 is a prime example of homophilic networking between regional neighbours with similar approaches to Ukraine, nurturing the transatlantic security relationship and beefing up NATO’s European pillar. The potential of the NB8 has been further enhanced by the recent participation of Poland – the ‘Sparta’ of East Central Europe – in the NB8 summit in Harpsund in December 2024, which underlined a renewed Polish engagement to the security of the Baltic Sea region.[12]
Discussions are now underway on expanding the remit of the Council of Baltic Sea States (CBSS) to include security and defence issues. The CBSS has the advantage of linking together the NB8 with Poland and Germany. Germany has also demonstrated a greater engagement with Nordic-Baltic security, both through its leadership of the FLF in Lithuania and the creation of the CTF[3] Rostock, which also underlines the German Navy’s new focus on Baltic Sea operations. Linking Germany with the Nordic-Baltic is important because the modernisation and expansion of the Bundeswehr promises to transform it into the future bulwark of conventional deterrence in Europe. The Trinity House agreement of 2024 has also strengthened bilateral security and defence cooperation between Germany and the UK, further weaving together the tapestry of deterrence in the Nordic-Baltic-North Atlantic region.
Another major element which facilitates the emergence of interlocking and overlapping synergies between Europe’s alphabet soup of defence cooperation is the UK-led JEF (Joint Expeditionary Force). This links the NB8 cluster with the UK and the Netherlands, and is the epitome of interstitial cooperation – agile, flexible and able to respond rapidly to crises in a coordinated manner. As one Royal Navy commodore put it ‘The JEF can act while NATO is thinking’. It is a ‘force of friends, filling a hole in the security architecture of northern Europe between a national force and a NATO force’.[13] British generals and ministers like to describe the JEF as ‘the beer-drinking nations of the North’, which underlines that it is also a prime example of homophilic networking.[14]
In conclusion, two points can made. First, although much of the discussion of Europe’s evolving security architecture is – quite understandably – focused on its twin institutional pillars, the EU and NATO, the reforging of European deterrence and formulation of a grand strategy for Europe will not come from top-down initiatives from either of these rather ponderous and cumbersome multilateral organisations. Rather, it will come from below, from clusters of plurilateral partners and interstitial defence cooperation. These looser and more flexible groupings are currently providing the political energy and practical cooperation that is signalling new strategic resolve in Europe. Plurilateralism and interstitial cooperation constitute the ‘hidden wiring’ of the Euro-Atlantic community, and provide the life-blood and vital juices that animate the EU and NATO.
Secondly, the most important and potentially influential plurilateral grouping in Europe today is arguably the NB8 which – in cooperation with Poland, Germany and the UK – will be at the heart of reforging deterrence along NATO’s eastern flank and providing a ‘reassurance force’ for Ukraine. As Polish Prime Minister Donald Tusk said after the signing of the Swedish-Polish strategic partnership in November 2024, Poland and the NB8 states were a ’solid group of states in solidarity’ that ‘speaks and thinks identically, including on the most difficult issues, which certainly includes Russia’s invasion of Ukraine’. Strengthening the bonds between the northern Europeans and the Baltics, he emphasised, ‘will send an important message to Europe that, on this issue, we are like a fist’.[15]