The treaty provided for the organisation of military, economic, social and cultural cooperation among member states as well as a mutual defence clause.

The treaty was signed on 17 March 1948 by Belgium, France, Luxembourg, the Netherlands and the United Kingdom, the members of the Western Union, as an expansion to the Treaty of Dunkirk, which had been signed between Britain and France the previous year to guard against possible German or Soviet aggression after the end of World War II.

[8] The treaty was intended to provide Western Europe with a bulwark against the communist threat and to bring greater collective security.

[10] Field Marshal Bernard Montgomery (UK) was appointed permanent Chairman of the Land, Naval and Air Commanders-in-Committee, with headquarters in Fontainebleau, France.

The nominated commanders-in-chief were General Jean de Lattre de Tassigny (France) as C-in-C, Land Forces, Air Chief Marshal Sir James Robb (UK) as C-in-C, Air Forces, and Vice-Admiral Robert Jaujard (France) for the Navy, as Flag Officer Western Europe.

Western Europe, therefore, sought a new mutual defence pact involving the United States, a powerful military force for such an alliance.

In December 1950, with the appointment of General Eisenhower as the first Supreme Allied Commander Europe (SACEUR), the members of the Treaty of Brussels decided to merge the Western Union Defence Organisation (WUDO) into NATO.

Trying to avoid the need for West German rearmament, a treaty aimed at establishing a European Defence Community was signed by the six ECSC members in May 1952 but failed when it was rejected by the French National Assembly in August 1954.