Fifteen years ago today (Wednesday), ten countries joined the European Union in the bloc's largest single expansion to date.
The new member states were Cyprus, the Czech Republic, Estonia, Hungary, Latvia, Lithuania, Malta, Poland, Slovakia and Slovenia.
European Commission President Jean-Claude Juncker said in a statement on Tuesday that "the decision in 2004 to embrace ten European countries was a great moment for our continent and a great moment in history."
"The accession of the Central and Eastern European countries, and the courage of their people in preparing for that accession, is what allowed us to reconcile our continent's geography with its history. I remain an ardent fan of enlargement today," he added.
According to figures released by the European Commission, the bloc will, by 2020, have invested €365.2 billion in these ten countries since their accession.
GDP per capita increases
Since their accession, GDP per capita — which divides a country's gross domestic product by its total population — has risen in all these countries.
Baltic countries — Estonia, Latvia and Lithuania — seem to have benefitted the most with GDP per capita doubling in all of them.
Unemployment meanwhile has declined in every country except Cyprus where it shot up from 4.9% in 2004 to 11.1% in December 2017.
Population changes present a more nuanced picture. The bloc counted 457 million inhabitants in 2004, whereas over 512 million people now live in the EU. The difference can partly be explained by the accession of three other member states since then — Bulgaria and Romania in 2007 and Croatia in 2013 as well
But in six of the ten countries which joined the bloc in 2004, the number of inhabitants has decreased. These are Estonia, Hungary, Latvia, Lithuania, Poland and Slovakia.
According to the Vienna Institute for Demography of the Austrian Academy of Sciences (ÖAW) and the Wittgenstein Centre, while Western European population continues to grow, "many countries of Eastern and South-eastern Europe are shrinking at an alarming rate."
Their research highlights that in Bulgaria, Latvia, Lithuania, Moldova, Bosnia-Herzegovina and Kosovo, population losses since 1990 have surpassed 20%.
The two main factors driving this difference are the balance of births and deaths, and international migration.
"Migration movements have now become the driving force behind the growth and decline of Europe's population," Tomáš Sobotka, a demographer for the Vienna Institute for Demography, said.