The Incomplete Union: Structural Weaknesses and the Limits of the Euro

The introduction of the euro marked one of the most ambitious projects of economic integration, aiming to promote efficiency, stability, and convergence across European economies. Yet from the very beginning, questions arose about how complete this monetary union really was. The lack of adequate fiscal, financial, and adjustment mechanisms cast doubt on whether the single currency could be sustainable over the long run. Using Optimal Currency Area (OCA) theory as a framework, this article argues that the Eurozone’s structural weaknesses made it vulnerable to asymmetric shocks and imbalances. The Eurozone crisis made this ever more clear, as financial integration heightened rather than smoothed the divergence between core and peripheral economies. Persistent structural differences in financial systems across member states continue to translate into unequal economic outcomes, reinforcing the idea that without deeper fiscal coordination and more integrated capital markets, the long-term stability of the monetary union will continue to be questioned.

To understand why these weaknesses emerged, it is worth examining the theoretical framework that anticipated them. Ever since the inception of the Eurozone, it has been well understood that the fiscal, financial, and monetary institutions required for a sustainable currency union were not sufficiently developed in Europe. This weakness can be understood through the theory of Optimal Currency Areas (OCA) proposed by Mundell, which defines the conditions under which adopting a single currency within a geographic region enhances economic efficiency and stability. According to OCA theory, countries that consider membership in a currency union are faced with a trade-off. They forgo national monetary policy but gain from increased economic efficiency, viz. lower transaction costs, price transparency, stimulated aggregate demand and trade. However, the main challenge arises from asymmetric shocks. Some countries experience a boom, others a recession. In a currency union, a single monetary policy cannot concurrently stabilize all economies, which means that policy changes that benefit some countries can come at the expense of others.

The OCA theory offers a set of criteria with which to assess a country’s suitability for partaking in a currency union. These criteria can be divided into two groups - those that reduce the likelihood of asymmetric shocks, and those that facilitate adjustment when such shocks occur.

The criteria that reduce exposure to asymmetric shocks are the following: similarity of economic structure, openness of trade and a low degree of specialization. Countries with similar economic structures are more likely to experience comparable business cycles. A high level of trade between members increases economic interdependence, making shocks more likely to affect all countries in a similar way. Finally, a low degree of specialization (Kenen criterion) implies that a member state is less vulnerable to the impact of sector-specific shocks.

The second group of criteria focuses on adjustment mechanisms: homogeneity of preferences, factor mobility and transfer payments. High labour mobility allows workers to move between regions, which restores equilibrium in the labour market by reducing regional unemployment differences; similar economic and political preferences among member states facilitate the coordination of policy responses to economic shocks. Lastly, transfer payments can support the recovery of depressed countries by redistributing resources from stronger to weaker economies.

The Eurozone does not currently represent an optimal currency area, as it performs poorly on several of the abovementioned criteria. Member countries differ in terms of economic performance and structure. Moreover, the common currency induced greater industrial specialization, which increased the vulnerability of the euro area to asymmetric shocks. Further, the European Monetary Union’s ability to act is restricted, as national preferences regarding decision-making and crisis management differ substantially. Lastly, adjustment mechanisms such as labour mobility and fiscal transfers remain limited.

These shortcomings were not merely theoretical. In the years leading up to the Euro crisis, these structural flaws led to persistent imbalances within the Eurozone. Some countries accumulated large external deficits, while others built surpluses. Not having the ability to adjust exchange rates, deficit countries were forced to devalue internally with expenditure reducing policies, which led to rising unemployment and reduced demand. This was politically and socially costly. These imbalances were closely linked to the pattern of financial integration within the Eurozone in the years preceding the crisis.

One of the main benefits to entry into the Economic and Monetary Union (EMU) was the more deeply integrated financial market within the member states. Following the introduction of the euro, cross-border capital flows increased substantially, as investors from core countries such as Germany, France, and the Netherlands reallocated funds towards Eurozone periphery nations like Ireland, Portugal, Spain and Greece. However, these capital flows were not efficiently allocated. A great proportion of them was invested in non-tradable sectors, such as housing and government consumption, rather than towards productive, export-oriented industries. This meant assets were not being created to help pay off the debt. It also tended to drive up wages and prices, which reduced the competitiveness of exports, leading to further worsening of the peripheral countries’ current accounts, i.e., net borrowing from abroad.

When the Eurozone crisis began, triggered by the Global Financial Crisis, the cross-border capital flows stopped. Countries that had relied heavily on foreign borrowing faced severe financial stress, as banks, and with that governments, weakened. Concerns about sovereign debt intensified.

The crisis exposed a fundamental asymmetry within the Eurozone. All countries that required financial assistance had previously accumulated large current account deficits, while surplus countries remained mostly unaffected.

Given the Eurozone design, governments who got in trouble had no lender of last resort, as the ECB was explicitly forbidden from playing the role. Member states were issuing debt in a currency they did not control, limiting their ability to guarantee liquidity during the crisis. Investors started losing confidence and moved their assets to safer countries like Germany, which pushed the deficit countries’ interest rates to unsustainably high levels and further worsened the recession there. This dynamic transformed liquidity problems into solvency crises, illustrating the vulnerability of Eurozone countries to self-fulfilling market pressures.

Eventually, the ECB addressed this issue for the time being by introducing the Outright Monetary Transactions (OMT) programme in 2012, de facto acting as a lender of last resort in sovereign bond markets. This intervention helped stabilize financial markets, but it did not resolve the underlying structural weaknesses of the monetary union.

Yet stabilizing markets was not the same as fixing the union’s deeper problems. A more persistent issue remained, namely the structural heterogeneity of financial systems across the Eurozone. In particular, differences in how firms and economies are financed, whether through banks or capital markets, play a crucial role in shaping how monetary policy is transmitted and how economies react to shocks.

A key dimension of this structural divergence lies in the financial architecture of Eurozone economies. As shown by Esposito et al. (2021), the Eurozone is characterized by a clear divide between bank-based finance (limited to loans granted by Monetary Financial Institutions (MFIs)) and market-based instruments (listed as equities, debt securities and investment fund shares).

The figure below illustrates important cross-country differences between the two types of financing considered. More specifically, we are able to observe that northern and core euro-area countries (Anglo-Saxon, Nordic, Germany, France, Benelux) have much higher shares of market-based finance, while most southern and peripheral EA members remain primarily bank-based.

Market Share and Bank Share in 2019

Source: Esposito et al. (2021) elaborations based on Eurostats and ECB Statistical Datawarehouse

Next, we bring our attention to the figure below, more precisely, on the EA12N and EA12S subgroups, which represent the core and the periphery of the EA, respectively. It is evident that market-based finance recorded a faster cumulative dynamic relative to bank-based finance both at the aggregate (EU28) and at the individual level of the subgroups considered. Bank credits (MFI loans) fell especially in EA12S (periphery countries) during both of the examined periods after the financial crisis, reflecting the credit crunch in the South. This evidence underscores how bank dependence makes these economies more vulnerable when financial conditions tighten.

Financial Sources of Non-Financial Corporations: cumulative changes

Source: Esposito et al. (2021) elaborations based on Eurostats and ECB Statistical Datawarehouse

The consequences of this financial divide extend well beyond the transmission of monetary policy. According to EU data, in the last decade innovation performance has increased, however, innovation divide is still present. The performance groups tend to be geographically concentrated, with the innovation leaders being in Northern and Western Europe, and the weaker performers, located in Southern and Eastern Europe.

It is logical to conclude that regions with greater access to capital markets, North and West, end up being innovation leaders, whereas the South and East ones, which have a weaker financial structure end up falling into the lower innovator categories. When the ECB tightens its monetary policy, the shock does not spread evenly across the euro area. Bank-dependent peripheral economies reduce their investment due to the deterioration in the lending conditions. Meanwhile, the core economies can lean on the capital market and their stronger innovation system, which better positions them to sustain investment.

These structural weaknesses also constrain the ability of peripheral economies to finance the green transition. ECB research highlights that meeting Europe’s long term climate targets requires deep capital markets and a substantial risk-bearing capacity, which is a feature that, as we have seen, is more common in the core than in the periphery. In the bank-dependent South, green investment is more sensitive to tightening in the financing conditions, meaning that contractionary monetary policy slows their decarbonization progress. Therefore, without deeper capital markets, the green transition risks becoming another channel through which regional heterogeneity intensifies.

These compounding disadvantages, slower investment, constrained innovation, and a lagging green transition, do not go unnoticed by the populations living through them. Uneven regional economic outcomes stemming from the divergence of the monetary policy, heighten perceived inequality. Evidence from the European Central Bank suggests that countries and regions with higher income inequality tend to have lower trust in the ECB, especially in times of crisis. This loss of confidence could have a detrimental impact on the institution’s legitimacy, as public trust is of relevance both for the anchoring of inflation expectations, which increase the effectiveness of monetary policy, and to shield the bank from political pressures that could undermine its independence.

These outcomes underline the need to complement monetary policy with institutional mechanisms capable of supporting convergence rather than allowing divergence to deepen.

Addressing this erosion of trust requires more than communication, it requires structural reform. A single monetary policy in the union has to navigate through heterogeneous fiscal policies, which generates fragmentation risks and unequal transmission. The asymmetric shocks that members are exposed to, can distort competitiveness within the European single market as regions experiencing economic downturns may struggle to compete with those less affected. One possibility to resolve this, as the ECB working paper “Marrying fiscal rules & investment” proposes, can be the introduction of a permanent central fiscal capacity (CFC). The purpose of such a mechanism would be to provide a central aid to regions hit by negative economic shocks, supplementing their national fiscal policies and, therefore, promoting macroeconomic stabilization, public debt sustainability and public investment.

Many policymakers, institutions and academics share the view that the European governance framework will remain incomplete without the establishment of a CFC, however, the precise design is still debated. Kenen et al. (1969) and later Farhi & Werning (2017) argued that fiscal integration is critical to a well-functioning currency union, concluding that international fiscal transfers in response to asymmetric shocks enhance macroeconomic stabilization in a currency union. This article’s broader argument is reinforced. Without a euro-area fiscal instrument, the peripheral economies that are facing tighter fiscal constraints and greater investment lags, will remain more exposed to contractionary monetary shocks, which in turn will continue to widen the divergence between the core and the periphery.

Concern that arises with the introduction of a CFC is the possibility of moral hazard in the form of weakened incentives to improve national economic resilience. However, well-designed fiscal rules can mitigate this risk, allowing a central fiscal capacity to function as a convergence tool without undermining fiscal responsibility.

Nevertheless, a central fiscal capacity alone cannot guarantee a balanced monetary union as the euro area’s divergence is not only fiscal but also financial. As we have mentioned, Europe has a very fragmented and uneven capital markets, which limits firms’ ability to smooth shocks and invest during downturns. This is why the completion of the Capital Markets Union (CMU) is essential.

The concept of a Capital Market Union (CMU) is to integrate and develop a unified capital market across the EU, which would ensure that abundant private capital is available for investment across the members’ borders. As it stands, the European Central Bank is bearing the disproportionate responsibility of having its monetary policy be the only stabilizing tool during crises. A completed CMU would correct this imbalance by enabling private capital to cushion shocks before they translate into monetary-policy divergence and would thus reduce the need for aggressive ECB interventions.

Currently, firms in the bank-dependent periphery economies are more vulnerable to ECB tightening, as local banks restrict lending more harshly. A completed CMU would mitigate this by enabling these firms to issue corporate bonds or raise equity EU-wide, strengthening private risk-sharing. As a result, investment would fall by less in the periphery, reducing the North-South divergence gap.

To conclude, the euro area’s divergence is not a feature of monetary integration but a consequence of the incomplete fiscal and financial architecture. Viewed through the lens of OCA theory, these are not optional enhancements, they are the missing criteria that the Eurozone’s founders chose to defer and that remain unresolved today. The reforms discussed above, central fiscal capacity and an integrated Capital Market Union, are tools that can ensure that monetary policy affects members more evenly and that investment is not geographically fragmented. Completing these economic pillars would allow the euro to function as intended, a source that supports long-term cohesion and prosperity within the union.

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