The North Atlantic Treaty Organisation (NATO) was formed on 4 April 1949, when twelve founding nations signed the North Atlantic Treaty (also called the Washington Treaty) in Washington, D.C. The founding members were the United States, Canada, the United Kingdom, France, Belgium, the Netherlands, Luxembourg, Norway, Denmark, Iceland, Italy, and Portugal.
NATO was established as a collective defence alliance in response to the growing threat posed by the Soviet Union and the spread of communism in Europe after the Second World War. The core principle of the alliance is contained in Article 5 of the treaty, which states that an armed attack against one member shall be considered an attack against all.
The other dates do not correspond to NATO's formation. 1945 marks the end of the Second World War and the founding of the United Nations. 1947 is associated with the Truman Doctrine and the Marshall Plan. 1951 saw the establishment of NATO's military command structure, but the organisation itself had already been created two years earlier.
