In welchem Jahr trat Österreich der Europäischen Union bei?

Why this is the correct answer

Austria joined the European Union on 1 January 1995, following a national referendum in June 1994 in which nearly two-thirds of voters approved membership. Joining ended Austria's post-war policy of permanent neutrality from Western economic blocs. Membership brought Austria into the EU's single market, common regulations, and eventually the Eurozone in 1999.