Western Union (alliance) followed by Supreme Headquarters Allied Powers Europe
The Western Union (WU), also referred to as the Brussels Treaty Organisation (BTO), was the European military alliance established between France, the United Kingdom (UK) and the three Benelux countries in September 1948 in order to implement the Treaty of Brussels signed in March the same year. Under this treaty the signatories, referred to as the five powers, agreed to collaborate in the defence field  as well as in the political, economic and cultural fields.
During the Korean War (1950–1953), the headquarters, personnel and plans of the WU's defence arm, the Western Union Defence Organisation (WUDO), were transferred to the newly established North Atlantic Treaty Organization (NATO), providing the nucleus of the European half of NATO's command structure (Allied Command Europe), led by Supreme Headquarters Allied Powers Europe (SHAPE). As a consequence of the failure of the European Defence Community in 1954, the London and Paris Conferences led to the Modified Treaty of Brussels (MTB) through which the Western Union was transformed into the Western European Union (WEU) and was joined by Italy and West Germany. As the WEU's functions were transferred to the European Union's (EU) European Security and Defence Policy (ESDP) at the turn of the 21st century, the Western Union is a precursor of both NATO and the military arm of the EU.