The Three Seas Initiative: Infrastructure and Geopolitics

The Three Seas Initiative (3SI) was launched in 2015 on the initiative of Croatia and Poland and now brings together 13 countries located between the Baltic, Adriatic and Black Seas. Formally, it aims to develop transport, energy and digital connectivity, particularly by addressing the long-standing infrastructure deficit along the north–south axis.¹⁶ Yet its geopolitical function cannot be understood solely as a European development policy.

From Intermarium to the Contemporary 3SI

The historical framework for understanding this space is provided by Intermarium, the Polish geopolitical concept developed in the interwar period around linking the states between the Baltic, Black and Adriatic Seas in order to contain Russian, and later Soviet, power in Eastern Europe. Today’s 3SI is not a revival of Intermarium, and the two projects should not be conflated. Nevertheless, their geographical overlap and their emphasis on north–south connectivity point to the enduring geopolitical significance of this same strategic space.¹⁷

3SI and NATO: An Informal but Significant Link

From the outset, the contemporary 3SI has had a strong transatlantic dimension. The United States became its strategic partner, while the U.S. International Development Finance Corporation agreed to provide up to $300 million for the Three Seas Initiative Investment Fund. The investment was justified in terms of energy security, energy diversification and improved regional connectivity.¹⁸

It is important, however, to distinguish the 3SI from NATO. The 3SI is not a military alliance and is not institutionally part of NATO. Its formal mandate is economic and infrastructural. Yet infrastructure itself creates a link with the Alliance’s security policy. The 2024 3SI declaration explicitly refers to dual-use infrastructure — infrastructure serving both civilian and military mobility — and to its contribution to strengthening NATO’s eastern flank.¹⁹

In other words, the 3SI does not enter NATO as an institution; rather, its infrastructure becomes part of NATO’s broader security architecture. A railway, road, port or bridge can simultaneously serve as an instrument of economic connectivity and as infrastructure enabling the rapid movement of troops, equipment and logistics. This is not a hidden function of the 3SI. It is explicitly reflected in its strategic documents.

Infrastructure built to promote economic connectivity thus simultaneously becomes part of the military mobility system and of a broader geopolitical push towards Russian territory.

The 3SI in a Broader Geopolitical Framework

This is why the Three Seas Initiative should be viewed within a broader geopolitical context. There is no need, however, to make Mackinder the central figure in the story. What matters is the broader tradition of Anglo-American geopolitical thought, which, since the late nineteenth century, has placed particular emphasis on control of the Eurasian space and on preventing the emergence of a unified continental bloc capable of becoming an autonomous centre of political, economic, and energy power.

Mackinder’s concept of the Heartland was one of the best-known formulations of this logic.²⁰ Following the decline of the British Empire, this strategic function was to a considerable extent assumed by the American strategic system. One can therefore speak of a continuity of Anglo-American geopolitical thinking, even though its instruments and institutional framework have changed.

From this perspective, the objective was not to create Europe as a fully autonomous geopolitical pole, but to prevent the consolidation of a continental space in which Russia could emerge as the dominant actor. After the Second World War, and particularly after the collapse of the Soviet Union, this logic did not disappear. It acquired a new institutional vocabulary: energy diversification, strategic resilience, connectivity, military mobility and reducing dependence on Russia.

After 2022, this was accompanied openly by the strengthening of NATO’s eastern flank. NATO now officially describes Russia as the most significant and direct threat to the security of the Allies.²¹ In this context, 3SI infrastructure acquires additional strategic value. The corridors linking the Baltic, Adriatic and Black Seas are not merely economic routes. They also increase the capacity to move people, goods, energy and military equipment across the territory of NATO’s eastern flank.

Croatian Infrastructure in a New Geopolitical Moment

The acceleration of Croatian infrastructure development therefore cannot be viewed simply as a belated continuation of European modernisation. Croatia is finally acquiring the transport capacity it should have developed decades ago. Yet the timing of this acceleration is not geopolitically neutral.

Railways, motorways and ports are being developed precisely as the space between the Adriatic, Baltic and Black Seas is becoming integrated into the security architecture of NATO’s eastern flank. Croatia is directly involved in this process as a member of the EU and NATO, a co-founder of the 3SI and host of the summit held in Dubrovnik in April 2026. Through Rijeka, it also connects the Adriatic with Central European transport corridors.

Rijeka’s position is particularly important. The Adriatic port is part of a transport network linking Central Europe to global markets, but also of north–south corridors whose security dimension is becoming increasingly pronounced. Croatia is therefore acquiring infrastructure with simultaneous economic, energy and military-logistical value.

Infrastructure as Economic Value and Geopolitical Vulnerability

For decades, Croatia lagged behind in the construction of modern transport infrastructure. Today, European investment is allowing it to rapidly make up for that deficit. This is unquestionably an economic benefit.

Yet the same infrastructure, precisely because it is integrated into European and NATO military mobility, could become a strategic target in the event of a major European war. In the event of a potential Third World War, Croatia could finally acquire infrastructure that it would not be able to use for long. Its economic value could simultaneously become a source of geopolitical vulnerability.

Croatian infrastructure therefore acquires a dual function: economic, in relation to global markets, and strategic, in relation to NATO’s eastern flank and the space bordering Russia. European investment is thus not merely a development policy. An increasing share of this infrastructure also serves a security function.

This is particularly important for Rijeka, which is seeking to position itself as a gateway for international trade and to connect Central Europe with global markets. The port’s economic function therefore intersects with the security function of transport corridors. Croatia finds itself at the intersection of two functions that are not necessarily contradictory, but are certainly not without risk.

Croatia as NATO’s “Resonance Chamber”

Within this structure, Croatia occupies an unusually sensitive position. It is not a major military power. It has neither global capital nor a geopolitical strategy comparable to those of the great powers. Yet it occupies an important transport position and belongs to the key institutions shaping today’s security architecture: the EU, NATO and the 3SI.

Croatia therefore functions today as NATO’s resonance chamber. The Alliance’s strategic priorities are rapidly translated into domestic infrastructure, energy and security policies. At the same time, the country’s own capacity to assess their long-term consequences remains comparatively weak.

This phenomenon should not be viewed as a question of loyalty to the Alliance. Croatia is a NATO member, and its obligations stem from that fact. The problem lies elsewhere: alliance membership does not eliminate the need for an independent geopolitical strategy.

If infrastructure corridors are built according to military mobility priorities, if Croatia is incorporated into the security architecture of NATO’s eastern flank, and if energy links are being redirected in order to reduce dependence on Russia, the state should simultaneously possess its own centre of strategic thinking. These processes should be addressed as a whole, particularly because the port of Rijeka is positioning itself as a gateway to global trade flows.

Instead, Croatian politics often behaves as though being on the right side is sufficient. Brussels gets implementation. Washington gets loyalty. The Allies get readiness. The domestic public is presented with infrastructure as a development project. The geopolitical risk, meanwhile, remains almost invisible.

Europe is investing in infrastructure it has lacked for decades, which is in itself welcome. But the same infrastructure is simultaneously acquiring a function in the Atlantic strategic push towards Russian territory, to which Moscow is firmly opposed. Croatia is thus becoming part of a new geopolitical configuration without a clear national strategy for managing the risks involved — a configuration in which economic benefit and security vulnerability grow simultaneously.

The Coalition of the Willing and Croatia’s New Geopolitical Direction

Britain’s active positioning alongside Ukraine and in support of its Western orientation did not begin in 2022, or even in 2014. Its roots can be clearly traced to the Orange Revolution of 2004. Even before Ukraine’s presidential elections, the British Foreign and Commonwealth Office funded projects aimed at political participation, civil-society development and the preparation of free and fair elections. Particular support was provided to the Ukrainian Committee of Voters, whose volunteers were trained in independent election monitoring. The British government stated that, during the preceding 18 months, it had funded projects designed to create the conditions for democratic elections and had provided an additional £600,000 for the 2004 presidential elections.²²

Britain was therefore actively involved in the political and institutional environment from which the Orange Revolutionemerged, although there is no sound basis for claiming that Britain itself organised or engineered the revolution. Following the disputed presidential election, London, alongside other Western governments, supported the rerun of the election and Viktor Yushchenko’s victory. The British Parliament also debated Britain’s contribution to the electoral process and its election-observation mission.²³

This political direction continued after 2004. Following the Maidan protests and the political crisis of 2013–2014, the British government openly supported Ukrainian sovereignty and the country’s new institutions. After Russia’s annexation of Crimea in 2014, however, British support acquired an increasingly explicit security dimension.

In early 2015, the United Kingdom launched Operation Orbital, a military training mission for the Ukrainian armed forces. The British government explicitly stated that the mission had been launched at the request of the Ukrainian government to provide training and advice to the Ukrainian armed forces. The British Parliament confirmed that it was intended as a long-term programme to strengthen Ukraine’s military capabilities.²⁴

In other words, British policy towards Ukraine has a continuity that predates the annexation of Crimea: from support for democratic and electoral processes in 2004, through active political engagement during the 2013–2014 crisis, to direct military training of Ukrainian forces from 2015 onwards. Boris Johnson did not initiate this policy: he became British Prime Minister only in 2019. But as Prime Minister, he pursued and significantly deepened it.

Against the backdrop of the war between Russia and Ukraine, Croatia has now positioned itself as a prominent member of the Coalition of the Willing, which, under British leadership, does not shy away from co-belligerence in support of Ukraine (participation in a war without a formal declaration of war). It would therefore appear that the risks Croatia is assuming may outweigh the economic benefits of the transport and logistical infrastructure that the Coalition — through EU mechanisms — is helping it build.

This raises a broader question. Through Atlantic integration, Croatia has, theoretically speaking, reached a satisfactory level of democratisation. Yet there has been almost no public debate about the country’s new geopolitical direction. New, because these strategic orientations differ substantially from those publicly proclaimed when Croatia decided to join the Atlantic Alliance.

It is important, therefore, to recall what NATO enlargement looked like during the 1990s. Following the end of the Cold War and the dissolution of the Soviet Union, NATO enlargement into Central and Eastern Europe was not publicly framed as a policy of confrontation with Russia. On the contrary, an institutional framework for cooperation with Moscow was being developed at the same time, including the Partnership for Peace and the 1997 NATO-Russia Founding Act, through which NATO and Russia explicitly defined their relationship at the time as a partnership rather than one between adversaries. Today’s open antagonism between NATO and Moscow therefore represents a major shift in the geopolitical context in which Croatia decided to join the Atlantic Alliance.

Even more significant is the fact that the Croatian government very actively and publicly supports this policy, both within the Coalition of the Willing and within the 3SI, while simultaneously finding itself at odds with the Commander-in-Chief of the Croatian Armed Forces, the President of the Republic.

Two problems converge here. Croatia is increasingly adopting the strategic priorities of the Atlantic space without having conducted a serious public debate about the transformation of its own geopolitical position. At the same time, a domestic institutional conflict has emerged over key questions of security policy. Institutional membership in the Alliance is thus becoming more important than independent strategic thinking.

This is precisely where the thesis of Croatia as NATO’s resonance chamber is confirmed: what originates within the broader Atlantic security system is rapidly translated into Croatian policy, while the question of whether that policy corresponds to Croatia’s long-term interests is pushed into the background.

Yet this, apparently, does not concern our allies, all of whom present themselves as democracies.

References

16. Garding, Sarah E., and Derek E. Mix. The Three Seas Initiative. Congressional Research Service, IF11547. Updated March 19, 2025.

17. Bartoszewicz, Monika Gabriela. “Intermarium: A Bid for Polycentric Europe.” Geopolitics 28, no. 2 (2023): 795–819. DOI: 10.1080/14650045.2021.1973439.

18. U.S. International Development Finance Corporation. “DFC and the Three Seas Initiative Investment Fund Agree to Term Sheet for up to $300 Million in Financing.” June 20, 2022.

19. Three Seas Initiative. “Joint Declaration of the Ninth Summit of the Three Seas Initiative.” Vilnius, April 11, 2024; Three Seas Initiative. “Political Declaration of the 11th Three Seas Initiative Summit.” Dubrovnik, April 28–29, 2026.

20. Mackinder, Halford J. Democratic Ideals and Reality: A Study in the Politics of Reconstruction. London: Constable and Company, 1919.

21. NATO. “Deterrence and Defence.” NATO, 2026.

22. Foreign and Commonwealth Office. Human Rights Annual Report 2004. London: UK Government, 2005.

23. House of Commons. “Foreign and Commonwealth Affairs.” Hansard, December 14, 2004.

24. UK Ministry of Defence. “Ukraine: Operation Orbital.” House of Commons Written Ministerial Statement, October 12, 2015; UK Government. “UK Programme Assistance to Ukraine 2016–2017.” GOV.UK.