Maastricht Treaty — European Union Created

The Treaty on European Union, signed in Maastricht, Netherlands, transformed the European Communities into the European Union and created the three-pillar structure (Community, CFSP, and Justice & Home Affairs). It introduced EU citizenship, laid out the convergence criteria and timetable for Economic and Monetary Union (the euro), and substantially expanded the European Parliament's co-decision powers. Denmark initially rejected it in a referendum; after opt-outs were agreed, it passed in a second referendum in May 1993.