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).

[2] In his speech to the House of Commons on 22 January 1948, British Foreign Secretary Ernest Bevin called for the extension of the Treaty of Dunkirk to also include the Benelux countries, creating a Western Union.

[3] The object was to consolidate Western Europe to satisfy the United States and to give advance notice of the eventual incorporation of Italy, and then West Germany, into the Treaty.

The negotiating conference was held on 4 March 1948, a few days after the coup in Prague;[4] thanks to this, the three smaller countries were able to persuade the others to agree to the concept of automatic and immediate mutual assistance in the event of aggression, and to the idea of setting up a regional organization (a multilateral alliance in accordance with Article 51 of the Charter of the United Nations).

On 20 December 1950 the Consultative Council of the Brussels Treaty Powers decided to merge the military organisation of the Western Union into NATO.

[11] 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 transfer the headquarters, personnel, and plans of the Western Union Defence Organisation (WUDO) to NATO.

[13][14][15][16] Field Marshal Bernard Montgomery resigned as Chairman of WUDO's Land, Naval and Air Commanders-in-Chief Committee on 31 March 1951 and took the position of Deputy Supreme Allied Commander Europe (DSACEUR) on 1 April 1951.