On 13 May 2026, Bucharest hosted the Summit of the Bucharest Nine (B9) and the Nordic countries. Oana-Cosmina Mihalache argues that the reunion’s outcome was indicative of the format’s role in the architecture of European defence cooperation
In the wake of Russia’s 2014 invasion of Ukraine, and subsequent annexation of the Crimean Peninsula, countries on NATO’s Eastern Flank came together under a new format. The Bucharest Nine (B9), formed at the initiative of Romania’s and Poland’s heads of state in Bucharest in 2015, comprises nine countries from Central and Eastern Europe. Its other members – Bulgaria, Czechia, Estonia, Hungary, Latvia, Lithuania, and Slovakia – are all EU and NATO members. The B9, dedicated to security and defence coordination, brings unity in a region dominated by complex security challenges. But will it buckle up and adapt to trends in European defence cooperation?
The 13 May summit was a watershed moment. Post-summit outcomes will reveal whether the B9 can adapt to the new trend of pragmatic federalism that sees the EU prizing clustered and flexible defence cooperation formats, or whether it chooses expansion for its own sake. Poland and Romania invited Nordic countries to join the meeting. This will either enhance prospects for minilateral clusters or show that the B9 is merely bending to the diktat of expansion.
B9's raison d’être was to establish a mechanism for consultation and dialogue dedicated to common security challenges. The geopolitical reality at its founding influenced its aim of strengthening defence and deterrence on NATO’s Eastern Flank. Cleavages that cut along many lines, including ideological ones, have stood in the way of a common threat perception. The format long lacked what other regional groupings shared.
The aim of the B9 is to establish a mechanism for consultation dedicated to security challenges such as strengthening defence and deterrence on NATO’s Eastern Flank
For one, the Visegrad Four countries share the goal of cultural cohesion and establishing common values beyond their military, economic, or energy ambitions. The Nordic-Baltic 8 (NB8), which unites the Nordic Five and Baltic Three countries, is bound by a shared threat perception that holds Russia firmly to blame for breaching Ukraine’s territorial integrity.
The B9 format had to grapple with two forces that threatened its cohesion. One, the idea of a multi-speed Europe, started to gain traction in 2017. The other was Russia’s attempts to exploit cracks within NATO and employ grey-zone tactics to divide and rule. Far from adding another Jovian ring to the multiple fractures threatening the Eastern Flank, the B9 paved the way for a new centre of gravity in the alliance’s resolve, which moved a few inches to the East.
The 2016 NATO summit in Warsaw established the enhanced Forward Presence in the Baltic states and Poland. The summit also agreed to increase rapid-reaction capabilities, and augment focus on the Black Sea region. At a 2022 extraordinary summit in Brussels, NATO extended its forward presence along the entire eastern flank. This translated into four new battle-groups, in Slovakia (led by Czechia), Hungary, Romania, and Bulgaria.
Recent developments in EU security and defence integration are complementary to NATO’s collective defence framework. These have thrived via minilateral cooperation groups through differentiated integration. This is a mechanism based on coalitions of the willing that advance the defence integration process by pooling resources and collective will. Former Prime Minister of Italy Mario Draghi, who was also President of the European Central Bank, described this process of countries coalescing around shared interests as pragmatic federalism.
In the defence sector, this way forward can help tip the balance away from the two extremes of national aggrandisement faced with a lack of capabilities on the one hand, and, on the other, EU ambitions that lack democratic legitimacy.
By tapping into the potential of minilateral formats, the B9 can advance its security agenda, taking advantage of its member states' political will to achieve desired capabilities
By tapping into the potential of minilateral formats, the B9 can advance its agenda in security and defence, taking advantage of its member states' political will to achieve or enhance desired capabilities. Defence clusters that have managed to overcome European cooperation challenges include the Franco-Italian and Belgian-Dutch naval cooperation, the Dutch-German integrated armies project in the land domain, and the Joint Expeditionary Force, which now comprises ten members and aims to foster greater interoperability.
Some B9 members are already embedded in the latticework of clusters that foster defence cooperation. Poland, Czechia, and the Baltic countries seem to have taken the lead. Others, like Romania, are stepping up efforts to advance a joint drone production facility with Ukraine under the EU’s SAFE Mechanism. The B9 can be an ideal incubator for related projects between its members.
The B9 includes the top four defence spenders in NATO, and comprises almost a quarter of the total EU population. Poland is by far the largest investor in defence spending. It also borders Belarus and, like Lithuania, shares a land border with the Kaliningrad enclave. Romania shares the longest border with Ukraine of any EU and NATO member. The country is also the only B9 member bordering the Republic of Moldova.
Given the position of its members and the surrounding threat environment, the B9 can encourage projects on hybrid and asymmetric warfare as well as maritime security
Given the position of its members and the surrounding threat environment, the clusters that the B9 can encourage become evident. These can include projects on hybrid and asymmetric warfare as well as maritime security. Recent developments in Ukraine and other theatres have revealed new possibilities for the future of warfare. NATO can address these through the creation of new minilaterals that share the B9’s wider goals. If it keeps expanding in scope without taking concrete steps in defence cooperation, B9 risks becoming a colossus with feet of clay. If it chooses to follow the minilateral trend and harness the power of the few, it can become a heavyweight piece in the European defence cluster-puzzle.
