Why EU reform and enlargement belong together

The European Union survives and succeeds when it treats the ‘’goods’’ it produces – such as the single market, the single currency, the single financial space, or security – as ‘’common-pool resources.’’ These resources are shared and available but also scarce and susceptible to overexploitation, and must be actively and collectively governed. The governance of common-pool resources is necessarily more intrusive (leading to reform) and more inclusive (paving the way for enlargement) than that of club-like, looser inter-governmental arrangements. We argue that, for the European Union, getting leaner and larger - in other words reforming and enlarging - at the same time is not a contradiction; it is how the EU sustains itself.

Russia’s full-scale invasion of Ukraine on 24 February 2022 clarified this logic. Within months, the EU accelerated the enlargement track for Ukraine, Moldova, and Georgia. In parallel, leaders ignited a debate on institutional reform, decision-making, and market-state capacity. Many observers saw an overreach: Why initiate a complex accession process while redesigning rules and institutions amid security crisis? In our book, From Club to Commons: Enlargement, Reform and Sustainability in European Integration, we explain why this twin move is both necessary and similar to how the EU reacted in the past.

The core of the book is a simple shift in perspective. Rather than seeing the EU as a cosy “club” that can police its borders and ration benefits, we argue that the EU manages goods that are hard to exclude outsiders from and where one actor’s use can constrain others – the classic features of common-pool resources. Much like a fishery where overfishing by one fleet reduces the stock available to others, the EU struggles to limit non-member actors such as foreign firms and workers from accessing the single market’s opportunities once value chains, digital platforms, and labour mobility create de facto interdependence. When such resources come under strain, well-run communities do two things: they tighten governance to curb bad behaviour and free-riding, and they widen cooperation so that those who benefit also share responsibility for sustaining the system. That is the EU’s story – not just since 2022, but at every turning point in its history.

The economic case: from club goods to contested shared resources

The EU began life as a small group of countries pooling sovereignty to expand trade. Think of that early phase in “club” terms: high excludability, low rivalry. As the Single Market deepened and widened, those properties changed. It became progressively harder to exclude non-members from accessing European opportunities – supply chains, investment, standards, and skills – while rivalry over the benefits intensified among firms and workers inside and outside the EU. Success bred demand; demand created strain.

European policymakers did not stumble into this. They chose, repeatedly, to broaden access because openness delivers efficiency and prosperity. Trade and Cooperation Agreements in the 1990s and the European Neighbourhood Policy after 2003 were designed to extend the reach of European rules without necessarily extending membership. That worked – until it didn’t. Where engagement became dense and incentives diverged, surveillance and coordination among governments were not enough; getting key neighbours to internalise rules was the only way to keep the system sustainable. Enlargement, in other words, was the governance tool of last resort.

This is the logic of common-pool governance in the style of Elinor Ostrom, Nobel prize winner political scientist for her insights on how local communities respond to the threat of resource exhaustion. When resources face overuse or predation, successful communities respond by pulling together and building governance arrangements to ensure that those resources can be managed sustainably. In EU terms: more discipline and mechanisms for mutual surveillance among member states, such as fiscal and macroeconomic monitoring, coupled with inclusion of highly integrated neighbours. That is why EU deepening and widening have tended to travel together – and why they are doing so again.

The security case: deterrence by embedding

Security is often described as a public good. In practice, the EU’s contribution to European security behaves more like a ‘’common-pool resource’’ – less excludable than a club good, more rivalrous than a pure public good. The EU creates security by knitting economies and legal orders together so tightly that conflict is both less attractive and more costly. That strategy reconciled former antagonists among the six original member states and stabilised the continent for seventy years. It also deterred outsiders through geopolitical tactics: harming an integrated neighbour risks harming the EU itself.

Enlargement amplifies this deterrent effect. When the EU offers the prospect of membership to Ukraine, it raises its own stake in Ukraine’s survival and success. The signal is not merely symbolic. The more Ukrainian firms and citizens become embedded in Europe’s market, money, and financial space, the more credible European security commitments become – and the more necessary EU reform becomes to manage the added scale and complexity. If the EU wants sustainable security, it cannot stop at sanctions, equipment, and rhetoric; it must align institutions and membership with the realities of dense interdependence with candidate states.

Why “hunker down” is the wrong instinct

Conventional wisdom says that when threats multiply, systems should consolidate, slow down, and get back to basics. That intuition is comforting but wrong. Europe’s problem today is not simply too much activity; it is the mismatch between self-interest and collective interest under high demand. The EU is attractive – to students, investors, workers, firms, and governments — precisely because it offers valuable goods. That attraction generates competition and congestion. Left unmanaged, it produces the familiar “tragedy of the commons”: rules are bent, free-riding spreads, coordination breaks down, and performance sags.

The answer is not retreat but disciplined cooperation. In practical terms, that means simplification and streamlining where rules are needlessly complex, stronger enforcement where incentives tilt toward opportunism, and better burden-sharing so those who benefit also contribute. It also means partnering more tightly with non-members who are already deeply intertwined with European markets and security – and, where appropriate, formal enlargement to lock in shared responsibility.

Policy implications: get leaner and larger to stay sustainable

If the EU is managing common-pool resources, several implications follow.

First, reform and enlargement are complements, not trade-offs. The EU must tighten the governance of its core goods – market, money, financial stability, security, and beyond – through clearer rules, more credible enforcement, and faster, more predictable decision-making. That is the leaner part, leading to EU reform. At the same time, where neighbours are already de facto participants in these goods, the EU should carefully bring them into the system in structured ways – up to and including membership – so that incentives are aligned and responsibilities shared. That is the larger part, paving the way for EU enlargement.

Second, inclusion is a governance instrument. Inclusiveness is not about charity or geopolitics for its own sake. It is about making the system more robust by ensuring that those with the biggest impact on the EU’s resources, such as Ukraine, adopt the same disciplines. Enlargement is the maximal version of that logic; new forms of structured partnership, starting with a common procurement financial instrument such as the Security Action for Europe (SAFE) and including staged accession, can serve similar ends where full membership is not yet feasible.

Third, sustainability requires sequencing and prioritisation, not paralysis. The EU cannot individually target all rising external challenges at once, but it must keep its eye on what sustains the common-pool resources: competitiveness in the single market, credibility in the euro, resilience in the financial space, and strategic responsibility in security. Recent plans for strengthening Europe’s defense industry across the supply chain, such as ReArm Europe, all fit this frame.

From Club to Commons offers a causal account that connects these dots. The EU’s goods have become attractive and, in practical terms, only partially excludable; rivalry over access is also real. That is why the EU looks less like a tidy club and more like a complex system governing common-pool resources. The remedy for overuse and opportunism is not to barricade the doors, but to govern better – and to widen the circle of those who share in both benefits and burdens.

Read the book by Veronica Anghel and Erik Jones, From Club to Commons: Enlargement, Reform and Sustainability in European Integration, available as Open Access on Cambridge Core and on the EUI Research Repository Cadmus.

Tags: EU, Enlargement, EU integration, EU membership, European Union