The North Atlantic Treaty Organization (NATO) was established following World War II as a system of collective defense among allied nations. The organization was assembled as a result of the North Atlantic Treaty, which was signed in Washington D.C. on April 4, 1949.


The primary purpose of NATO is to ensure the protection of its members. It is a large and ever-growing alliance of countries that have sworn under the treaty to defend and consul their partners in times of need. Article 4 states that if “the territorial integrity, political independence or security of any of the parties is threatened,” other members will offer that country consultation on military matters.

Article 5 is possibly the most well-known element of the treaty. It states that any armed attack on a single NATO country is seen as an attack on all NATO allies. Article 4 has been invoked several times throughout history, but Article 5 has only been cited once, following the September 11, 2001 attacks in the United States.


The organization born of the North Atlantic Treaty was formed by eleven European countries and the United States. Following the dissolution of the Soviet Union and the falling through of the Warsaw Pact, NATO took on a new, humanitarian-driven purpose in addition to its initial goals. Since its inception, the organization has expanded well beyond the boundaries of Europe and the United States. As of March 2019, NATO includes 29 different countries, the most recent inclusion being Montenegro in 2017. In the near future, the organization will likely expand to include Bosnia and Herzegovina, Georgia, North Macedonia, and Ukraine. NATO also sponsors a Partnership for Peace program that includes 21 other countries and engages in institutionalized dialogue programs with 15 other nations. Both NATO headquarters, as well as that of Allied Command Operations, are located in Belgium.