A European Union member state is any one of the twenty-eight countries that have joined the European Union (EU) since it was found in 1958 as the European Economic Community (EEC). From an original membership of six states, there have been five successive enlargements. The largest happened on May 1, 2004, when ten member states joined.
Following the addition of Croatia in 2013, the EU's membership now stands at twenty-eight. Negotiations are also under way with other states. The process of enlargement is sometimes referred to as European integration. However, this term is also used to refer to the intensification of cooperation between EU member states as national governments allow for the gradual centralising of power within European institutions. Before being allowed to join the European Union, a state must fulfil the economic and political conditions generally known as the Copenhagen criteria: these basically require that a candidate member state must enjoy a secular, democratic system of government, together with the corresponding freedoms and institutions, and respect the rule of law. Under the terms of the Treaty on European Union, enlargement of the Union is conditional upon the agreement of each existing member state as well as approval by the European Parliament.