Introduction

The concept of diversity and heterogeneity may be considered one of the central features of the European Union (EU) and applies both to the economic and the political dimensions of the project of European integration. Economically, the four rounds of enlargements by 16 countries and the introduction of the common market program, in addition to the European Monetary Union (EMU), noticeably increased the heterogeneity of the EU. In just two decades, the addition of these countries moved the European Union from a free trade association of 12 countries with a population of approximately 380 million to a common market area of 28 countries (most of which have also joined the EMU) with a population of almost 600 million. Thus, among the 12 EU countries that were EU members in the late 1980s, the second wealthiest country (ignoring Luxembourg, which is the wealthiest of these 12 countries but is an outlier) in terms of GDP per capita at purchasing power parities (the Netherlands) was approximately 1.8 times wealthier than the poorest country under the same metric (Greece); however, among the 28 countries that are currently members of the EU (two decades later), the same ratio was 2.9.