NATO (the North Atlantic Treaty Organization) is an international alliance that consists of 29 member states from North America and Europe.
It was established at the signing of the North Atlantic Treaty on 4 April 1949. Article Five of the treaty states that if an armed attack occurs against one of the member states, it shall be considered an attack against all members, and other members shall assist the attacked member, with armed forces if necessary.
The member states of NATO are:
Albania, Belgium, Bulgaria, Canada, Croatia, Czech Republic, Denmark, Estonia, France, Germany, Greece, Hungary, Iceland, Italy, Latvia, Lithuania, Luxembourg, Montenegro, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Turkey, United Kingdom, United States.