The Maastricht Treaty, also known as the Treaty on European Union, was signed on February 7, 1992. It became active on November 1, 1993, during the Delors Commission. It established the European Union and led to the creation of the Euro. It was amended by the treaties of Lisbon, Nice, and Amsterdam.
Upon creation, the European Union was comprised of three pillars: the European Communities, which dealt with economic, social, and environmental policies, the Common Foreign and Security Policy, which handled foreign policy and military matters, and the Police and Judicial Co-Operation in Criminal Matters, which focussed on law enforcement and fighting crime. The three pillar structure was abandoned on December 1, 2009, when the Treaty of Lisbon became active.