The Western Union (WU), also referred to as the Brussels Treaty Organisation (BTO),[1] 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.[Note 1] 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.