This is a 28 (soon to be 27) member political union. The history is complicated but whilst many point to the European Coal and Steel Community (ECSC) as the starting point of the EU, this is only partially true as you have to look at the brain behind the project. One Jean Omer Marie Gabriel Monnet and one Jean-Baptiste Nicolas Robert Schuman, who were essential to the creation of the ECSC and the further integration and expansion that precipitated from there.
The key goal at the start was to make war financially impossible by linking together the economies and industries of the various European countries. At the time in 1951 the founding members in the Treaty of Paris were; France, West Germany, Italy, Belgium, Luxembourg and the Netherlands. But most of the time people attribute peace as the main goal of the ECSC and whilst this to an extent was the case, many forget the basic ideologies of Monnet and Schuman. These being ones of ardent federalists intent on creating a "United States of Europe" as shown in a quote from Monnet on the 5th August 1943 to the National Liberation Committee (the French government of De Gaulle in exile in Algiers during WW2)
There will be no peace in Europe, if the states are reconstituted on the basis of national sovereignty... The countries of Europe are too small to guarantee their peoples the necessary prosperity and social development. The European states must constitute themselves into a federation...
From here 8 years before the founding of the ECSC you can clearly see the final intent of Monnet and those like Schuman who followed these ideas.
From here in the ECSC the first major supranational European institutions were formed. The High Authority would later become the European Commission and the Common Assembly would become the European Parliament. The first president of the High Authority was Jean Monnet himself. From here there were failed attempts to create defense and political communiites - of which the EU has succeded one the latter and is working on the former.
In the 1957 the 3 Treaties of Rome (often referred to together as the Treaty of Rome) of which the EU held a bittersweet 60th anniversary just days before the triggering of Article 50 on the 29th March 2017. These Treaties formed the European Economic Community (EEC). They also created the European Atomic Energy Community (Euratom) if people were wondering why this was referenced multiple times in Theresa May's Article 50 letter to the President of the European Council - Donald Tusk.
This is where the UK comes in. The UK tried to apply to join the EEC in 1963 and wasvetoed by Charles de Gaulle the French President (8th January 1959 - 28th April 1969). Then again in 1967 he vetoed the UK joining the EEC.
One can see the relevance of his words now after the UK voted to leave the EU:
England in effect is insular, she is maritime, she is linked through her exchanges, her markets, her supply lines to the most diverse and often the most distant countries; she pursues essentially industrial and commercial activities, and only slight agricultural ones. She has in all her doings very marked and very original habits and traditions
Looking back now you can see his point. The UK was never much involved in continental affairs compared to France and Germany. The UK went and created the largest empire known to mankind, even at its peak in 1920 without the 13 states the UK still was the dominant world power. The UK had gone off to the world and looked more outwards than what the EEC project demanded. So perhaps in retrospect de Gaulle was correct in vetoing the UK joining the EEC.
After his removal from power and his subsequent death in 1970 the UK applied again and joined alongside Denmark and Ireland on the 1st January 1973.
Then in 1981 Greece joined on the 1st January. This would become controversial as they were a much weaker economy, an issue that would rear its head in the Eurocrisis. Greece's level of debt and deficit were hidden by Goldman Sachs to allow it to join the Euro in 2001, which was seen as a trigger of the forthcoming Eurocrisis.
Greenland then left the EEC after gaining home rule from Denmark, so not a country leaving rather a territory. Spain and Portugal then joined on the 1st January 1986 in what was called the 3rd enlargement.
In 1986 the then Commission President Jacques Delors was in charge at the time of the adoption of the European Flag from the Council of Europe (not part of the EU). This was also the year of the SIngle European Act in February of that year. It dealt with the extension of the EECpowers and reform of the insitutions and layed the foundation of the SIngle Market.
Turkey applied in 1987 and still havent been accpeted even though negotiations are ongoing even as the Turkish governement is drifting away from many of the criteria for joining the EU especially in liberty, freedom and human rights areas.
In 1989 Germany was reunified after the fall of the Berlin Wall and the EEC expanded again.
Then on the 7th February 1992 the highly controversial Maastricht Treaty was signed. It transformed EEC into the EU, from an economic union into a political one. Monnet's and Schuman's vision was coming true.
Accession negitiations and talks with Austria, Sweeden and Finland finished on the 30th March 1994 and the EU expanded again. Then the countries of Norway, Iceland and Liechtenstein joined the European Economic Area allowing European Free Trade Association (EFTA) states to enter the Single Market.
Schengen (a free movement policy or no borders or checks) came into force in 1995 with 7 countries, soon encompassing almost all of the EU by the end of 1996. Key here was the UK's decision against joining, which some view as saving us from much of the ussues associated with free movement of people on the continent.
In 1999 the EU set about the next step of integration, being a single currency in the Euro. At the sane time the European Central Bank (ECB) was formed. This replaced participating members currencies on the 1st January 2002.
Then on the 26th February 2001 the Nice Treaty was signed, which came into force on the 1st February 2003. This was the preperation stage of the Eastward Expansion of 2004. The countries of Cyprus, Hungary, Estonia, Latvia, Lithuania, Malta, Poland, the Czech Republic, Slovakia and Slovenia. Then on the 25th April 2005 Bulgaria and Romania signed the Treaty of Accession which allowed them to join on the 1st January 2007.
Then when the EU tried to create a Consitiution the French and Dutch voted no in referendums and the project was shelved. However the Lisbon Treaty signed on the 13th December 2007 and entering into force on the 1st December 2009 was set out to "reform" the EU. But parts of the Constitution that the French and Dutch rejected seemed to have been worked into the Lisbon Treaty.
In 2007 Slovenia adopts the Euro, then in 2008 Malta and Cyprus and then in 2009 Slovkia followed.
In the UK the Prime Minister Tony Blair (Labour) full name Anthony Charles Lynton Blair had been trying to get public support for joining the Euro but failed. In a way saving the UK from being tied to the Eurocrisis directly, even if we did have to pour money in for bailouts of entire countries.
Over the next few years and possibly may continue for the foreseeable future the countries of Greece, Italy, Ireland, Spain and Portugal risked defaulting on debts, loans and commitments. The Eurocrisis was born. To this day none of these countries have fully recovered and it is looking like we are heading for a repeat, as if the Commission haven't learnt anything.
Then the final (as of 2017) country to join the EU was Croatia on the 1st July 2013.
Current candidates for joining the EU are; Albania, Macedonia, Montenegro, Serbia and Turkey. Potential future candidates include Bosnia and Herzegovina and Kosovo.
Switzerland, Norway, Iclenad and Liechtenstein are all countries in EFTA that are not part of the EU.
Andorra, Monaco, San Marino, Vatican City and Liechenstein all use the Euro but are not memebers of the EU.
Then in a great blow to the expansionist policies of the EU the UK voted on the 23rd of June 2016 to leave the European Union by a margin of 51.9% to 48.1%. Then with Article 50 of the Lisbon Treaty being triggered on the 29th March 2017 the UK will become the first (and possibly not last) country to leave the EU.
So Monnet and Schuman's vision of a United Federal States of Europe was rejected by the UK......will anyone follow?
Your views? Is there anything you wish to add, challenge or correct me on?