The North Atlantic Treaty Organization (NATO) is an alliance based on the principle of collective defence stated in the North Atlantic Treaty signed in Washington on April 4th 1949.

Article V of the Treaty states that an attack on one member country is  perceived  as an attack on the whole Alliance and calls on member states to assist one another in case of dispute.

The member states of NATO are: Albania, Belgium, Bulgaria, Canada, Croatia, Czech Republic, Denmark, Estonia, France, Germany, Greece, Hungary, Iceland, Italy, Latvia, Lithuania, Luxembourg, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Turkey, United Kingdom, United States.