The EU is a three-pillar structure of the original supranational European Economic Community and the nuclear non-proliferation treaty, Euratom, plus two largely intergovernmental pillars dealing with External Affairs and Justice and Home Affairs. The EU is therefore not a "de jure" federation, although some academic observers conclude that after 50 years of institutional evolution since the Treaties of Rome it is "becoming" one. The European Union possesses attributes of a federal state. However, its central government is far weaker than that of most federations and the individual members are sovereign states under international law, so it is usually characterized as an unprecedented form of supra-national union. The EU has responsibility for important areas such as trade, monetary union, agriculture, fisheries. Nonetheless, EU member states retain the right to act independently in matters of foreign policy and defense, and also enjoy a near-monopoly over other major policy areas such as criminal justice and taxation. Since the Treaty of Lisbon, the Member States' right to leave the Union is codified, and the Union operates with more qualified majority voting (rather than unanimity) in many areas.