North Atlantic Treaty Organization

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North Atlantic Treaty Organization: members and partners

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

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NATO summary

North Atlantic Treaty Organization

Q: Who has the largest army in NATO?

The United States has the largest army in NATO, with about 1.3 million personnel. Next on the list is Turkey with almost 450,000. The rest of the top five are France (200,000), Germany (180,000), and Italy (175,000). (Numbers are approximate.)

Q: When did the U.S. join NATO?

The United States joined NATO in 1949 as one of the 12 founding members. The others are Belgium, Canada, Denmark, France, Iceland, Italy, Luxembourg, the Netherlands, Norway, Portugal, and the United Kingdom.

Q: What is the purpose of NATO?

The purpose of NATO is to “to safeguard the freedom and security of all its members. It does this through political and military means.” The heart of NATO is expressed in Article 5 of the North Atlantic Treaty, in which the signatory members agree that: “an armed attack against one or more of them in Europe or North America shall be considered an attack against them all.” The alliance currently has 32 member countries.

Q: Has NATO’s Article 5 ever been invoked?

NATO’s Article 5 is central to the alliance. The signatory members agree that “an armed attack against one or more of them in Europe or North America shall be considered an attack against them all.” The article has only been invoked one time: in 2001, after the September 11 attacks organized by Osama bin Laden destroyed the World Trade Center in New York City and part of the Pentagon outside Washington, D.C., killing some 3,000 people.

Q: How many countries are in NATO?

Currently 32 countries are members of NATO: Albania, Belgium, Bulgaria, Canada, Croatia, the Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Italy, Latvia, Lithuania, Luxembourg, Montenegro, the Netherlands, North Macedonia, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Turkey, the United Kingdom, and the United States.

Q: What does NATO stand for?

NATO is an acronym for North Atlantic Treaty Organization.

Q: What is NATO?

The North Atlantic Treaty Organization (NATO) is a military alliance originally established in 1949 to create a counterweight to Soviet armies stationed in central and eastern Europe after World War II. When the Cold War ended, NATO was reconceived as a “cooperative-security” organization.

Q: Which countries are in NATO?

The 32 current member states of NATO are Albania, Belgium, Bulgaria, Canada, Croatia, the Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Italy, Latvia, Lithuania, Luxembourg, Montenegro, the Netherlands, North Macedonia, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Turkey, the United Kingdom, and the United States.

Q: What are the newest members of NATO?

Sweden is the newest member of NATO. It joined the alliance as its 32nd member in March 2024. Sweden announced its intention to join NATO in 2022, in response to Russia’s invasion of Ukraine , but its membership bid was held up for two years by objections from Turkey and Hungary. Finland joined NATO in April 2023, also in response to Russia’s invasion of Ukraine.

Also known as: NATO

Written by David G. Haglund

Fact-checked by The Editors of Encyclopaedia Britannica

Last Updated: Aug 7, 2025 • Article History

Quick Facts

Date:: August 24, 1949 - present

Areas Of Involvement:: defense; How does a country become a member of NATO?

Related People:: Dwight D. Eisenhower; Harry S. Truman; Konrad Adenauer; Mark Rutte; Joseph Dunford

See all related content

Who has the largest army in NATO?

When did the U.S. join NATO?

What is the purpose of NATO?

Has NATO’s Article 5 ever been invoked?

How many countries are in NATO?

What does NATO stand for?

What is NATO?

Which countries are in NATO?

What are the newest members of NATO?

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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. In Article 5, the signatory members agree that NATO invoked Article 5 for the first time in 2001, after the September 11 attacks organized by ...(100 of 2941 words)

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