The European Union (EU) is an international association of 27 European countries, most recently Croatia, which joined on July 1, 2013. It was founded on an agreement known as the Maastricht Treaty signed in 1992, but many of its ideas have been around since the 1950s.

One of the most important principles of the European Union is the transfer of the powers of nation-states to European international institutions. However, these institutions are still governed by the amount of powers granted by each individual state, so this union cannot be considered a federal union as it has a unique political system in the world.

The European Union has many activities, the most important being a single market with a single currency, the euro, which has been adopted by 19 of the 27 member states, a common agricultural policy, and a common fisheries policy. In March 2007, the EU celebrated its 50th anniversary with the signing of the Treaty of Rome. On October 12, 2012, the EU was awarded the Nobel Peace Prize for its contribution to the promotion of peace, reconciliation, democracy and human rights in Europe.

On June 23, 2016, the United Kingdom decided in a referendum to leave the European Union, becoming the first country to do so. The UK officially left the EU on January 31, 2020.