North Atlantic Treaty Organization

Introduction & Top Questions
Historical background
Organization
Membership
The role of Germany
The role of France
NATO during the Cold War
NATO in the post-Cold War era
- NATO in the former Yugoslavia and expansion into eastern Europe
- NATO relations with Russia in the post-September 11 world
- NATO and the Russian invasion of Ukraine

References & Edit History Quick Facts & Related Topics

Images

Flag of NATO featuring a white compass rose emblem with four lines radiating from the center on a blue background.

World map highlighting NATO member countries in dark blue, Euro-Atlantic Partnership Council countries in light blue, NATO's Mediterranean Dialogue partners in purple, Istanbul Cooperation Initiative partners in pink, and global partners in teal. Brussels, Belgium, is marked as NATO headquarters. A timeline below the map shows the years each member joined NATO from 1949 to 2024.

Secretary of State Dean Acheson sits at a table signing the North Atlantic Pact as President Harry Truman and Vice President Alben Barkley stand behind him, with officials observing.

Map of Europe in 1960 during the Cold War, showing countries color-coded by political alignment: NATO members in green across Western Europe, Warsaw Pact countries in orange in Eastern Europe, and non-aligned nations in beige. The Soviet Union and its allies are grouped to the east, while Western European countries are aligned with the United States.

flag-raising ceremony marking the accession of the Czech Republic, Hungary, and Poland to NATO

Jerzy Buzek, Miloš Zeman, Javier Solana, and Viktor Orbán at a ceremony marking the accession of the Czech Republic, Hungary, and Poland to NATO

Volodymyr Zelensky during the Russian invasion of Ukraine

Swedish Prime Minister Magdalena Andersson in a blue coat stands beside Finnish Prime Minister Sanna Marin in a black jacket outdoors before a meeting in Stockholm.

At a Glance

NATO summary

Quizzes

Yellow transportation sign with ASAP (as soon as possible) on violet color sky background. (acronyms)

Figure Out the Acronyms ASAP Vocabulary Quiz

Secretariat Building at United Nations Headquarters with Members States' flags flying in the foreground, United Nations Headquarters, New York City, New York. (photo dated 2017)

Global Governance Quiz

43 Questions About Politics (Mostly in the United States) Compiled from Britannica’s Quizzes

Related Questions

How did Britain’s and France’s nuclear forces differ within NATO during the Cold War?
How did NATO members fund military bases and other shared infrastructure during the Cold War?
How did NATO’s flexible response strategy change its approach to nuclear weapons?
How did Soviet control of central and eastern Europe influence the creation of NATO?
How did West Germany joining NATO lead to the formation of the Warsaw Pact?
How did the Dayton Accords lead to NATO peacekeeping forces in Bosnia and Herzegovina?
How did the Partnership for Peace program promote security in Europe?
How did the September 11 attacks lead NATO to take on missions outside Europe?
How did the communist takeover in Czechoslovakia in 1948 affect plans for a North Atlantic alliance?
How did the dual-key system control the use of U.S. nuclear weapons in Europe?
How does Article 5 of the North Atlantic Treaty establish collective defense?
How does a Membership Action Plan help a country prepare for NATO membership?
How does the North Atlantic Council govern NATO?
Under what circumstances can a NATO member invoke Article 4?
What are the roles of Allied Command Operations and Allied Command Transformation?
What concerns did opponents raise about NATO expansion into former Soviet-allied countries?
What obligations do NATO members have when another member is attacked under Article 5?
When did Albania and Croatia join NATO?
When did France return to NATO’s integrated military command?
When has NATO invoked Article 5?
When was the NATO flag adopted?
When was the North Atlantic Treaty signed?
Where are NATO’s Allied Command Operations and Allied Command Transformation headquartered?
Which 12 countries signed the North Atlantic Treaty in 1949?
Which countries joined NATO in 1999?
Which countries were NATO’s founding members in 1949?
Who serves on the North Atlantic Council?
Why did Finland and Sweden seek NATO membership after Russia invaded Ukraine?
Why did France leave NATO’s integrated military command in 1966?
Why did NATO conduct air strikes against Serbia during the Kosovo conflict in 1999?
Why did NATO develop cooperative links with Russia and Ukraine after the Cold War?
Why did NATO establish the North Atlantic Cooperation Council in 1991?
Why did NATO invoke Article 5 after the September 11 attacks?
Why did NATO use military force in Bosnia and Herzegovina in 1995?
Why did North Macedonia’s path to NATO membership take more than 20 years?
Why did some people question whether NATO was needed after the Warsaw Pact dissolved in 1991?
Why has defense spending created disagreements among NATO members?
Why must every NATO member approve a new country’s accession protocols?
Why was Dwight D. Eisenhower chosen as NATO’s first Supreme Allied Commander Europe?
Why was Sweden’s NATO membership delayed until 2024?
Why was West Germany’s membership in NATO controversial in the 1950s?
Why was the North Atlantic Treaty Organization created after World War II?
Have two NATO countries ever gone to war against each other?
Can the president pull the U.S. out of NATO?
What is NATO’s Article 4?
What is the purpose of NATO?
Has NATO’s Article 5 ever been invoked?
What are the newest members of NATO?
Who were the monuments men and women?
Was The Monuments Men a true story?
What are the Japan Self-Defense Forces (JSDF)?
How powerful are the Japan Self-Defense Forces (JSDF)?

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External Websites

The Balance - What is NATO?
North Atlantic Treaty Organization - Kosovo Air Campaign (March-June 1999)
Council on Foreign Relations - What Is NATO?
Official Site of North Atlantic Treaty Organization

Britannica Websites

Articles from Britannica Encyclopedias for elementary and high school students.

North Atlantic Treaty Organization - Children's Encyclopedia (Ages 8-11)
North Atlantic Treaty Organization (NATO) - Student Encyclopedia (Ages 11 and up)

North Atlantic Treaty Organization

military alliance

Also known as: NATO, OTAN, Organisation du Traité de l’Atlantique Nord(Show More)

Written by

David G. Haglund

Director, Centre for International Relations, Queen's University, Kingston, Ontario, Canada. Author of Alliance Within the Alliance?: Franco-German Military Cooperation and the European Pillar of Defense,...

David G. Haglund

Fact-checked by

Britannica Editors

Encyclopaedia Britannica's editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree....

Britannica Editors

Last updated

Nov. 13, 2026 •History

North Atlantic Treaty Organization (NATO), military alliance established in 1949 that sought to create a counterweight to Soviet armies stationed in central and eastern Europe after World War II. Following the end of the Cold War, NATO was reconceived as a “cooperative-security” organization. It has 32 member states. The heart of NATO is expressed in Article 5 of the North Atlantic Treaty (also called the Washington Treaty), which founded the alliance on April 4, 1949....