Enlargement of the European Union

• 1. Introduction

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  The Enlargement of the European Union tells the story of one of the most ambitious political projects in modern history: a community that began with six founding nations in 1958 and has since grown to twenty-seven members, reshaping the map and politics of an entire continent. When the Treaty of Rome came into force that year, the Inner Six were pooling coal and steel. By 2004, former Soviet-bloc countries were signing accession treaties. How does a club that started among France, West Germany, Italy, Belgium, Luxembourg, and the Netherlands expand to include Estonia, Poland, and Slovenia in a single morning? What criteria must a country meet, and what does the process actually look like from the inside? And why, even after decades of remarkable growth, has the door swung shut on some applicants while remaining tantalizingly ajar for others?

• 2. Rules of the Club

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  At the Copenhagen summit in June 1993, EU leaders codified what it actually takes to join. The resulting Copenhagen criteria require a stable democratic government that respects the rule of law, a functioning market economy capable of competing within the single market, and the willingness to adopt the entire existing body of EU law, known as the acquis communautaire. That last requirement alone runs to tens of thousands of pages of regulations, directives, and standards accumulated over decades. In December 1995, the Madrid European Council added a further condition: candidate countries must not only adopt European legislation but also build the administrative and judicial structures to enforce it effectively at home.

  The formal accession process begins long before a country submits an application. A prospective member typically first signs an association agreement designed to prepare it for candidacy. When the formal application arrives, the Council asks the European Commission to assess whether the country is ready to begin negotiations. That opinion can be overridden; the source notes that only once has the Council rejected a commission recommendation, when it overruled advice against opening talks with Greece. If negotiations are approved, a chapter-by-chapter screening process follows, examining where a candidate's laws diverge from EU standards. Chapters can be re-opened even after they are declared closed, if the commission decides the country has fallen out of compliance. The entire journey from application to membership has typically taken about a decade, though Sweden, Finland, and Austria moved much faster. Turkey, by contrast, first sought association in the 1950s and still had not concluded accession negotiations as of the time the source was written.

• 3. Early Expansions and Vetoes

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  Robert Schuman's declaration on the 9th of May 1950 proposed pooling French and West German coal and steel, and within two years Belgium, Luxembourg, the Netherlands, and Italy had joined to sign the Treaty of Paris on the 23rd of July 1952. The United Kingdom had declined to participate as a founder. After the Suez Crisis changed British calculations, London sought to join, but French President Charles de Gaulle vetoed that application. Only after a twelve-hour conversation between British Prime Minister Edward Heath and French President Georges Pompidou did Britain's third attempt succeed. Heath marked the occasion by saying he had no doubt the discussions would prove of real and lasting benefit, not only to Britain and France, but to Europe as a whole. Denmark, Ireland, and Norway applied alongside the UK; Norway's government, however, lost its national referendum on membership and did not join when the others acceded on the 1st of January 1973. Gibraltar entered the Community alongside the United Kingdom at the same moment, as reflected in the long title of the UK European Communities Act 1972.

  Algeria presented a different kind of territorial drama. As an integral part of France, Algeria had a special relationship with the Community from the start. When Algeria gained independence on the 5th of July 1962, it left the Community by that same act. Greenland would follow a different path: in 1985 it used newly granted home rule from Denmark to vote its way out, becoming the first territory to leave the Community through a popular vote.

• 4. The Southern Democracies

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  Greece, Spain, and Portugal each emerged from dictatorship during the 1970s, and their desire to anchor their fragile new democracies within European institutions drove the next wave of enlargement. The EEC, for its part, wanted stability along its southern borders and sought to ensure these neighbors did not slide back toward authoritarian rule. François Mitterrand initially opposed all three memberships, fearing the former dictatorships were not ready and that their inclusion would dilute the community into a free-trade area. Despite that resistance, Greece joined in 1981, followed by Spain and Portugal in 1986. None of the three held a referendum related to accession.

  In 1962, Spain, then ruled by Francisco Franco, had made its first attempt to join the Communities. Foreign Affairs minister Fernando María Castiella had sent the request to French Prime Minister Maurice Couve de Murville. All member countries rejected it in 1964 on the grounds that Spain was not a democracy. It took another generation and a change of regime before Spanish membership became possible. Morocco also applied in 1987, but its application was turned down because Morocco was not considered a European state. Turkey applied the same year; while its application was considered eligible under the 1963 Ankara Association Agreement, the commission's opinion at that point was negative.

• 5. The Big Bang of 2004

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  Mikhail Gorbachev's announcement in the late 1980s that the Soviet Union would no longer intervene in other countries' internal affairs effectively freed Central and Eastern Europe from Soviet-backed regimes. Countries like Czechoslovakia and Hungary moved quickly toward democratic governance and soon looked west. The EU struggled initially: the collapse of communism was sudden and unanticipated, and the bloc was already grappling with German reunification, which on the 3rd of October 1990 added East Germany and its poorer population of roughly seventeen million people to the Community without changing the formal count of member states.

  The US added its own pressure, encouraging EU expansion as a temporary guarantee of stability while preferring to move more cautiously on NATO enlargement, out of concern about provoking Russia. In the end, the EU conducted accession talks with ten countries simultaneously. Eight Central and Eastern European countries, the Czech Republic, Estonia, Hungary, Latvia, Lithuania, Poland, Slovakia, and Slovenia, joined alongside Malta and Cyprus on the 1st of May 2004. That single day represented the largest enlargement in history measured by the number of countries and total population, though not by GDP. Some older member states, including the UK, immediately opened their labor markets to citizens of the new members; most others imposed temporary restrictions that lasted until 2014 in some cases. The movement of workers westward generated public debate in some western countries, including the phrase "Polish plumber" used in media of the time. Romania and Bulgaria, judged not fully ready in 2004, acceded instead on the 1st of January 2007.

• 6. The Balkans and the Frozen Cases

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  Croatia became the most recent full member to join, acceding on the 1st of July 2013 following ratification of its 2011 Accession Treaty by all other EU countries. The 2003 European Council summit in Thessaloniki had established integration of the Western Balkans as a priority, and in 2005 EU relations with the region moved formally from the External Relations policy segment into the Enlargement directorate. All successor states of the former Socialist Federal Republic of Yugoslavia have since adopted EU integration as a stated aim of foreign policy.

  Turkey's case stands apart. Negotiations were opened in October 2005 but have been effectively frozen by the EU since December 2016, after the commission determined that Turkey had been backsliding on democracy, the rule of law, and fundamental rights. Former Commission President Romano Prodi had already suggested a different model for states that cannot join outright, proposing to grant them "everything but institutions," allowing deep cooperation without straining the EU's governance structures. France and Germany have backed a version of this idea as a privileged partnership for Turkey.

  On the 6th of February 2018, the European Commission published an expansion plan covering all six Western Balkan applicants, envisaging that each could achieve membership after 2025. As of the latest updates in the source, Montenegro's accession negotiations are the most advanced among current candidates; the country has declared its political goal of achieving EU membership by 2028, and it is the only current candidate to have reached the interim benchmarks for chapters 23 and 24 that allow the closing process to begin across all negotiation chapters.

• 7. Ukraine, Georgia, and New Frontiers

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  The 2022 Russian invasion of Ukraine triggered a fast-track response from EU institutions. Ukraine, Moldova, and Georgia all submitted membership applications in the aftermath. On the 17th of June 2022, the European Commission recommended that Ukraine and Moldova receive candidate status; Georgia was proposed as a potential candidate subject to conditions including reforms in elections, judicial independence, anti-corruption efforts, and policies toward oligarchs. These recommendations were approved by the European Council at a summit on the 23rd of June 2022.

  On the 14th of December 2023, the European Council formally granted candidate status to Georgia and agreed to open accession negotiations with Ukraine and Moldova. Then, on the 9th of July 2024, the EU halted Georgia's accession process after Georgian authorities adopted a new foreign influence law that raised concerns about democratic freedoms. Bosnia and Herzegovina and Georgia had been granted candidate status in December 2022 and December 2023 respectively, but each was asked to complete additional reforms before formal negotiations could begin. Kosovo submitted its own application in December 2022; five EU member states do not recognize its independence, meaning the Council cannot yet unanimously agree to start its accession process. Armenia presents yet another new direction: on the 26th of March 2025, the Armenian parliament approved a bill initiating the formal process of EU accession, following a European Parliament resolution in March 2024 confirming Armenia meets the eligibility requirements of Article 49 of the Maastricht Treaty.