The members of the North Atlantic Treaty Organization (NATO) entered into a defensive alliance, with the main agreement being that they would come to the aid of any member of NATO that was attacked by the Soviet Union or its allies.
NATO was formed in 1949. Its original members were Belgium, the Netherlands, Luxembourg, France, the United Kingdom, the United States, Canada, Portugal, Italy, Norway, Denmark and Iceland.
Today, NATO has 29 member nations. After the demise of the Soviet Union and its alliance organization, the Warsaw Pact, NATO's focus has shifted somewhat. But NATO remains a powerful organization in international politics.