Migration remains one of the most divisive issues in European politics, consistently ranking among voters top concerns. Most attention focuses on arrivals from outside the EU. Yet large migratory flows within the Union have profoundly reshaped both the receiving and the sending countries, economically and socially, and are often overlooked in discussions about the evolution of the European project.
The Schengen Agreement, originally signed in 1985, heralded the abolition of internal borders among participating countries (currently 29 member states), beginning in 1995. Nevertheless, of greater pertinence was the signing of the Maastricht Treaty in 1992, which established that all EU citizens have the right to free movement across the entirety of the EU.
In 2023 Bulgaria recorded the worlds second-fastest population decline, behind only war-torn Ukraine, a continuation of a long downward trend.1 EU membership in 2007 accelerated outward migration, and when labour-market restrictions disappeared in 2014 the exodus quickened.2 Today roughly one-quarter of all Bulgarians live abroad, most of them of working age, with severe consequences at home.3
Health care illustrates the damage: Bulgaria has the EUs worst nurse-to- patient ratio because a third of newly trained nurses and about 40% of the countrys doctors now practise abroad.4 Overall, high-skill flight costs the economy an estimated 0.7 percentage points of GDP each year (OECD modelling).5 The loss feeds a vicious circle of dwindling confidence Bulgarians who remain often question the states future despite the country’s rich culture, appealing landscape and favourable climate.
Polands early post-accession experience looked similar. After joining the EU in 2004, millions of Poles seized the chance to work and study in other member states, most visibly in the United Kingdom.6 Alongside migrants from fellow Central- and Eastern-European entrants, this east-to-west wave upended expectations. Despite earlier debates focusing on non-EU migrants, the sudden influx dominated Britains media cycle. Right-leaning outlets leveraged the newcomers as proof of unchecked EU influence, stoking Eurosceptic sentiment that would ultimately help propel the 2016 Brexit vote.7
The large net outflow created shortages of nurses akin to Bulgaria’s current experience, and the loss of working-age residents was palpable. One key difference, however, is that the Polish economy proved more robust; it absorbed and even benefited from wage pressure, lifting living standards for workers and, indirectly, pensioners as an appreciating zoty made imports cheaper.8
The trend reversed, and by 2019 Poland had moved into net immigration.9 Many Poles returned with skills and savings accumulated abroad. The turnaround coincided with rapid GDP growth already visible by 2016, partly spurred by Brexit-related emigration from the UK but not limited to it.10 Governance also mattered: in 2016 Transparency International ranked Poland 35th worldwide,11 and efficient absorption of EU funds reinforced investor confidence.12 Although later judicial disputes dented that record, Poland still scores around the EU average on corruption metrics and continues to attract both returning citizens and foreign workers.
Between 2016 and 2019 Poland averaged 4 percent real GDP growth, a pace that aligned closely with the reversal of its migration balance.13 The comparison with Bulgaria underscores a key lesson: when wage convergence, sound institutions and active return policies align, a brain drain can become brain circulation, turning emigration from a liability into an engine of domestic growth.
Other member states that joined the EU in the 2000s lie somewhere between the extremes of Poland and Bulgaria. Lithuania recorded its first positive migration balance in 2019,14 Latvia is effectively neutral,15 and Bulgarias northern neighbour Romania posted its first ever surplus in 2022/23.16
The 2004 and 2007 enlargements had striking effects on the main receiving states, notably the United Kingdom, Germany, Ireland and the Netherlands. In Britain the number of Polish nationals alone reached about one million by 2016, making Poles the countrys largest foreign nationality group.6 These migrants filled acute shortages in construction, food processing, hospitality and the National Health Service; a UCL study found they paid £45 billion more in taxes than they drew in services between 2004 and 2011.17
Germany posted similar gains, as East-European workers kept factories fully staffed and limited wage-driven inflation during the mid-2010s boom.18 In Ireland, East-European immigrants accounted for nearly a quarter of all new labour-force entrants in the decade to 2015, easing demographic pressure.19 Across the host economies the evidence is clear: East European migrants boosted GDP, helped finance ageing welfare systems and demonstrated the non-zero-sum nature of intra-EU mobility despite modest, localised wage pressures at the low-skill end.
Alongside their economic contributions, East-European arrivals have intro- duced a host of new culinary and cultural touches to supermarket aisles and high streets. Today youll find Polish kiebasa and pierogi alongside German sausages, Romanian zacusc and Bulgarian sirene cheese in major chains.20 Often Tescos supermarkets in the UK have their own Polish isles including sweets and sausages alike. Beyond food, local councils host Slavic folk dance workshops and events such as the Balkan Traffic festival in Brussels.21
Despite the evident benefits, one should also consider how internal EU mi- gration is perceived. Generally speaking, internal EU migrants are held in higher esteem than those coming from non-EU countries, as highlighted by a 2024 Eurobarometer survey which saw EU migrants being viewed favourably (67%) compared to non-EU migrants (46%).25
When viewed negatively, one common trope is that migrants are more likely to commit crime. There is sparse research distinguishing between non-EU and EU migrants with regard to their criminal activities. However, in the German context, once a migrant’s socio-economic status is taken into account, immigrants as a whole are no more likely to commit crimes than German citizens, with their overall overrepresentation largely reflecting the higher concentration of the immigrant population in urban areas.26
Thus far internal migration has been overall favourable to the EU both socially and economically despite attempts by right wing outlets to suggest to the contrary.
The story of intra-EU migration over the past two decades reveals a dynamic, mostly self-correcting system. Initial east-to-west flows relieved unemployment in the sender states and powered growth in the receivers; over time, rising wages, return incentives and institutional reforms began to pull workers back east. It remains to be seen in the Bulgarian case if the benefits will be fully realised though this is likely simply a matter of time and a greater willingness to drive down corruption.
Nevertheless, climate stress now threatens to push new waves northward from the Mediterranean that may be a far more sinister affair. A 2023 Nature Communications model coupling sea-level-rise exposure with population flows projects up to 20 million internal movers across the Mediterranean basin by 2100 if no adaptation occurs.22 Most net emigration originates from Spain, Italy, Greece and Croatia, while in-migration concentrates in higher elevation urban corridors stretching into France, Germany, Belgium and the Netherlands, although the latter is itself threatened by sea-level rise.
Eurofound assessments show that heat stress driven productivity losses will rise three-to-four times faster in Southern than in Northern Europe, reinforcing the economic pull towards cooler labour markets.23 Already in 2023 olive oil output fell by 40,24 and the Joint Research Centres July 2024 briefing on persistent droughts warned of critical water shortages menacing crops in Spain, Portugal, southern Italy and Greece.24
Despite much of recent internal shifts in population having been mutually favourable, without bold measurements the level of future migration may be on a vastly different scale with little to no benefit to sender countries. If climate driven migration is not mitigated the possible internal strife may end up being the biggest threat to the European project.