The European Union is a political and economic union of 27 European countries established after World War II to promote cooperation and shared values among member states. Key events included the Treaty of Rome establishing the European Economic Community in 1957, the Maastricht Treaty founding the EU and introducing the euro in 1992, and the Lisbon Treaty reforming decision-making in 2007. The EU's main institutions are the European Commission, European Parliament, European Council, and European Central Bank. The EU works on policies related to the single market, agriculture, fisheries, border control, research, the environment, and more. It faces challenges including Brexit, economic issues, migration, rule of law concerns, and nationalism within member states.