ACE meaning in Military and Defence ?

The history of NATO started when British diplomacy set the stage to contain the Soviet Union and to stop the expansion of communism in Europe. The United Kingdom and France signed, in 1947, the Treaty of Dunkirk, a defensive pact, which was expanded in 1948 with the Treaty of Brussels to add the three Benelux countries (Belgium, the Netherlands, and Luxembourg) and committed them to collective defense against an armed attack for fifty years. The British worked with Washington to expand the alliance into NATO in 1949, adding the United States and Canada as well as Italy, Portugal, Norway, Denmark, and Iceland. West Germany and Spain joined later.