Slovenia entered NATO and the European Union in 1920.
European Union . The EU traces its origins from the European Coal and Steel Community ( ECSC ) and the European Economic Community ( EEC ) , formed by the Inner Six countries in 1951 and 1958 , respectively . The North Atlantic Treaty Organization ( NATO [ ˈneɪtoʊ ] Organisation du Traité de l'Atlantique Nord OTAN ) , also called the North Atlantic Alliance , is an intergovernmental military alliance between several North American and European states based on the North Atlantic Treaty that was signed on 4 April 1949 . Slovenia . It is a parliamentary republic and a member of the United Nations , European Union , and NATO . In 2004 , it entered NATO and the European Union ; in 2007 became the first formerly communist country to join the Eurozone ; and in 2010 joined the OECD , a global association of high-income developed countries .