The North Atlantic Treaty Organisation (NATO) is a military alliance that consists of 32 member states from North America and Europe. It was established at the signing of the North Atlantic Treaty on Apr. 4, 1949.  Article Five of the treaty states that if an armed attack occurs against one of the member states, it should be considered an attack against all members, and other members shall assist the attacked member, with armed forces if necessary.

Of the 32 members of NATO, two are North American countries and 30 are European countries. The founding members include Belgium, Canada, Denmark, France, Iceland, Italy, Luxembourg, Netherlands, Norway, Portugal, United Kingdom and the United States.

The most recent member nation is Sweden which joined the Alliance on March 7, 2024.