WASHINGTON—In April, the Three Seas Initiative celebrated its tenth anniversary in Dubrovnik. In the historic Croatian port city, the initiative’s thirteen member states, all of which are located between the Adriatic, Baltic, and Black Seas, marked the occasion with a summit and business forum focused on increasing connectivity across the region. In addition to representatives from Three Seas member states, participants from more than two dozen other countries, including from as far away as Japan, attended the two-day gathering.
The high turnout shows how successful the Three Seas Initiative has been in engaging policymakers, business leaders, and investors well beyond the geographic triangle to which its name refers. But even with the initiative’s expanding global influence, there has been little serious discussion within the initiative about expanding official membership. That should change.
Historically, Three Seas membership has been limited to European Union (EU) member states, which excludes several countries in the Western Balkans and Eastern Europe from joining. There is a rationale behind this requirement: EU membership carries with it an expectation of political stability and order, which are necessary to attract the significant investment needed to achieve the initiative’s mission of deepening connections in the region. As a result, Greece, which was admitted in 2023, is the only new member to join the initiative since its founding.
Importantly, no formal charter or bylaws require the Three Seas Initiative to admit only current EU members; adherence to this practice is more a matter of political will and process than a rigid statute. Yet the practice has nonetheless proven inflexible, and the initiative has pursued half-measure workarounds. In lieu of full membership, the Three Seas Initiative has extended associate membership to Albania, Moldova, Montenegro, and Ukraine. It has been a step in the right direction to reassure EU candidates as they work toward accession, though largely a symbolic move.
But as the initiative moves into its second decade, it will likely find such partial measures harder to sustain because they leave holes in its larger goals. Associate membership gives Albania, Moldova, Montenegro, and Ukraine a seat near the table, but not necessarily a full role in setting priorities, shaping corridors, attracting capital, or determining which projects define the region’s long-term infrastructure map.
Instead, the Three Seas Initiative should take steps to elevate its associate members to full members while deepening connections with the rest of the region.
Why membership matters
The Three Seas was founded with a mission of building a Europe that is whole and prosperous. A major impediment to this goal is decades of underinvestment in north-south infrastructure to connect countries in Central and Eastern Europe. By working to connect digital, energy, and transportation infrastructure, the initiative aims to expand the region’s economic potential, which has grown significantly in recent decades.
But there is another objective beyond economic output: developing dual-use infrastructure that can help secure Europe’s eastern flank against an aggressive Russia. For example, railways that are traditionally used for transporting goods can be repurposed to move military materiel along the eastern front if needed. Similarly, improved regional digital networks and cybersecurity infrastructure can provide the basis for deterring cyberattacks. In essence, the Three Seas is creating a proverbial wall between Europe and Russia.
Looking at the map of Three Seas Initiative members, it quickly becomes clear that the initiative is missing core components in Ukraine, Moldova, and the Western Balkans. Without a robust north-south corridor, NATO and Europe are left with a noticeable hole in their armor in terms of deterring or defending against Russia. As associate members play a limited role in shaping projects, they are not thoroughly incorporated into plans from the beginning, closing a window of opportunity to address these gaps.
In Ukraine’s case, this debate is not hypothetical—sharing borders with four Three Seas members and Russia, Ukraine is pivotal to securing the wider region. Acting now to bring Ukraine into the initiative stands to strengthen the transatlantic dimension, sending a clear signal to Vladimir Putin that Ukraine is part of Europe already.
In the Western Balkans, prospective Three Seas members may not neighbor Russia, but the Kremlin has sought to interfere with pro-European paths and maintain influence to strengthen its so-called sphere of influence. In this regard, supporting the Western Balkans in developing Western digital and energy infrastructure could reduce the risk of Russian cyberattacks or energy sabotage in those countries and across the region.
Beyond Russia, China has similarly sought to build influence in the Western Balkans, including through its Belt and Road Initiative. From 2009 to 2021, China invested more than €32 billion in the region, with a substantial amount of that investment falling within the initiative’s purview of digital, energy, and transportation infrastructure. Denying China the ability to develop a greater foothold in Europe should be high among the initiative’s objectives, given its geopolitical framing. Deeper integration of Western Balkan states into the initiative, especially as full members, would do precisely this.
A commercial case for Ukraine
At its heart, the Three Seas is a commercial initiative that leverages high growth rates, rich human capital, and significant investment returns to mobilize funding for infrastructure projects. The initiative’s neighbors can tangibly contribute to its economic prospects by widening the pool of viable infrastructure corridors and investment opportunities.
Toward this end, Ukraine offers a unique case due to its hefty reconstruction needs, which are currently estimated at nearly $600 billion. Once the war ends and funding for Ukraine’s rebuilding begins to flow in, the Three Seas should expand its connection to newly developed Ukrainian infrastructure.
The right time to act
The Three Seas Initiative aims to close a longstanding infrastructure gap created by decades of underinvestment. Non-member countries in the region face the same problem. Without deepening involvement with Ukraine, Moldova, and more of the Western Balkans, the initiative simply shifts the underinvestment problem to other countries, perpetuating the underlying investment gap within Europe.
Instead of creating a greater infrastructure disparity between EU member states and candidate states, the Three Seas should support these countries on their path toward EU membership by beginning to integrate them economically now. Furthermore, the right time to incorporate new members is not after a crisis hits, as was the case with Ukraine and Moldova becoming associate members after Russia’s 2022 invasion of Ukraine. Bringing in new members now, before a crisis, can help reduce the chance of future instability.
Note: The Atlantic Council’s work on the Three Seas Initiative surrounding the 2026 Dubrovnik Summit and Business Forum, including this article, is supported by the government of Croatia. The Atlantic Council maintains strict intellectual independence across all of its projects and publications. This analysis represents the author’s views alone.