Number of member states of the EU 1957-2023

The European Union is a supranational organization founded in 1957 (under the name European Economic Community) currently comprised of 27 European states, which aims to facilitate economic and political cooperation on the European continent. The current member states of the EU, in alphabetical order, are: Austria, Belgium, Bulgaria, Croatia, Cyprus, Czechia, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, the Netherlands, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, and Sweden. Additionally, the United Kingdom was a member of the EU from 1973 until 2020, with the country voting to leave the European Union in 2016. There are currently also eight candidate countries (countries in the process of joining the EU): Albania, Bosnia & Herzogovina, Moldova, Montenegro, North Macedonia, Serbia, Turkey, and Ukraine; as well as two potential candidates, Georgia and Kosovo.

The Founding Six: 1957

The European Economic Community was founded through the 1957 Treaty of Rome by Belgium, France, Germany, Italy, Luxembourg, and the Netherlands. The six countries were united by the aim of integrating their economies together in such a way which would provide economic prosperity on the European continent and to prevent future conflicts from arising between the countries. This was particularly informed by the French and German politicians, who wished to prevent their countries going to war, as they had done three times over the preceding century (1870-71, 1914-18, and 1939-45). The treaty is considered fundamental to the functioning of the European Union, with the famous statement at its beginning that the countries were seeking to pursue "ever closer union".

The First Enlargement: 1973

In 1973, additional countries joined the European Community for the first time. Denmark, Ireland, and the United Kingdom joined the community on the 1st of January 1973, with Ireland and Denmark having held referendums during 1972, with 83 percent voting in favor in Ireland and 63 percent voting in favor in Denmark. Norway had planned to join along with the three other countries, however, their citizens rejected the proposal in a referendum with 54 percent voting against it. The United Kingdom held a referendum in 1975, two years after joining, in which its citizens confirmed the government's decision to join, with 67 percent voting in favor. The UK had been an applicant to join the community since 1963, but had been blocked by French President Charles de Gaulle numerous times, due to his suspicions that the British were too influenced by the United States.

The Southern Enlargement: 1981-1986

In 1981 Greece became the first of three southern European countries who had recently transitioned from military dictatorship to democracy to join the European Community. Greek democracy had been restored in 1975, following seven years of rule by a military junta. Portugal and Spain later joined in 1986, as the Carnation Revolution of 1974 had moved Portugal towards free, multi-party elections, while the death of Spain's long-serving dictator General Francisco Franco in 1975 opened up the space for democracy to re-emerge. Some European politicians were hesitant to admit countries with such short histories of democracy and lower living standards than the rest of the bloc, however, there was also a desire to integrate these countries and to prevent a slide back towards authoritarianism.

The Third Enlargement: 1995

In 1995, Austria, Finland, and Sweden became the next three countries to join the European Union (the Maastricht Treaty of 1992 had renamed the EEC to the EU). These three countries had a long history of cooperation with EU countries, being closely tied historically and culturally to certain member states (Sweden and Finland to Denmark, and Austria to Germany), as well as having been long-standing members of the European Free Trade Association (EFTA), an organization which facilitates the economic integration of non-EU countries with the EU. Norway had once again planned to join along with these three states, however, its citizens rejected the proposal with 52 percent voting against in a 1994 referendum. The same occurred in Switzerland, whose voters rejected joining the EU by a razor-thin margin, with 50.3 percent voting against.

The Eastern Enlargement: 2004-present

Since 2004, 13 countries have joined the European Union, almost doubling the size of the bloc. The 2004 enlargement is often referred to as the 'eastern enlargement' as eight post-communist states in central and eastern Europe (Czechia, Estonia, Hungary, Latvia, Lithuania, Poland, Slovakia, and Slovenia) joined. Alongside these countries, the Mediterranean island states of Cyprus and Malta also joined the EU in 2004. Later, in 2007 Bulgaria and Romania became the next post-communist countries to join, while Croatia became the second country from the former Yugoslavia (a communist country in south-eastern Europe which comprised 7 current countries) to join in 2013. Currently seven countries in eastern and south-eastern Europe are in the process of joining the EU, including four former Yugoslavian states (Bosnia & Herzogovina, Montenegro, North Macedonia, and Serbia), Albania, Moldova, and Ukraine. Negotiations with Turkey are currently frozen due to concerns over democratic backsliding and human rights abuses, while Georgia and Kosovo have applied to become candidates in the future.