Representatives from the United States, Canada, and ten Western European nations signed the North Atlantic Treaty at the State Department, formalizing a collective defense pact aimed squarely at deterring Soviet expansion. Article 5's mutual-defense clause became the alliance's cornerstone. NATO would go on to shape the entire architecture of the Cold War and, decades later, expand eastward to include many former Warsaw Pact states.
The treaty's signing came less than a year after the Berlin Blockade had rattled Western capitals and convinced American and European leaders that a formal military alliance, not just economic aid through the Marshall Plan, was needed to contain Soviet ambitions. Secretary of State Dean Acheson had spent months negotiating the treaty's language, particularly Article 5, which committed members to treat an attack on any signatory as an attack on all — a radical departure from America's historic aversion to permanent military entanglements in Europe.
The twelve founding members — the US, Canada, Britain, France, Belgium, the Netherlands, Luxembourg, Norway, Denmark, Iceland, Portugal, and Italy — gathered in Washington's Departmental Auditorium. President Truman told the assembled diplomats that the pact was 'a shield against aggression.'
NATO's first Secretary General, Lord Ismay, later quipped that the alliance's purpose was 'to keep the Russians out, the Americans in, and the Germans down.' The organization would trigger Article 5 for the first and only time not during the Cold War, but after the September 11, 2001 attacks on the United States.