The Western European Union Decides to Gradually Transfer its Responsibilities to the EU

The Treaty of Lisbon includes a collective defense clause [Article 42(7) of the EU Treaty] within the framework of the European Union’s Common Security and Defense Policy (CSDP) rules. When an EU member state is the subject of an armed attack on its territory, other member states must assist it by any means at their disposal. These commitments must be consistent with the commitments made by member states as NATO members.
Article 42(7) of the EU Treaty is based on the Brussels Treaty (as amended in 1954) under which the Western European Union (WEU), a defense alliance of 10 Western European countries, was established. Together with the North Atlantic Treaty Organization, these formed the main guarantor of European security after World War II. On November 13, 2000, in Marseille, the WEU Council of Ministers agreed to gradually transfer its capabilities and tasks to the CSDP, which is an integral part of the Common Foreign and Security Policy (CFSP). Eventually, the WEU ceased to exist in June 2011.