Collective defence and Article 5 (2023)

  • Last updated: 20 Sep. 2022 13:23
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The principle of collective defence is at the very heart of NATO’s founding treaty. It remains a unique and enduring principle that binds its members together, committing them to protect each other and setting a spirit of solidarity within the Alliance.

Collective defence and Article 5 (1)

  • Collective defence means that an attack against one Ally is considered as an attack against all Allies.
  • The principle of collective defence is enshrined in Article 5 of the Washington Treaty.
  • NATO invoked Article 5 for the first time in its history after the 9/11 terrorist attacks against the United States.
  • NATO has taken collective defence measures on several occasions, including in response to the situation in Syria and the Russian invasion of Ukraine.
  • NATO has standing forces on active duty that contribute to the Alliance’s collective defence efforts on a permanent basis.
  • A cornerstone of the Alliance

    Article 5

    In 1949, the primary aim of the North Atlantic Treaty – NATO’s founding treaty – was to create a pact of mutual assistance to counter the risk that the Soviet Union would seek to extend its control of Eastern Europe to other parts of the continent.

    Every participating country agreed that this form of solidarity was at the heart of the Treaty, effectively making Article 5 on collective defence a key component of the Alliance.

    Article 5 provides that if a NATO Ally is the victim of an armed attack, each and every other member of the Alliance will consider this act of violence as an armed attack against all members and will take the actions it deems necessary to assist the Ally attacked.

    Article 5

    “The Parties agree that an armed attack against one or more of them in Europe or North America shall be considered an attack against them all and consequently they agree that, if such an armed attack occurs, each of them, in exercise of the right of individual or collective self-defence recognized by Article 51 of the Charter of the United Nations, will assist the Party or Parties so attacked by taking forthwith, individually and in concert with the other Parties, such action as it deems necessary, including the use of armed force, to restore and maintain the security of the North Atlantic area.

    Any such armed attack and all measures taken as a result thereof shall immediately be reported to the Security Council. Such measures shall be terminated when the Security Council has taken the measures necessary to restore and maintain international peace and security.”

    This article is complemented by Article 6, which stipulates:

    Article 61

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    “For the purpose of Article 5, an armed attack on one or more of the Parties is deemed to include an armed attack:

    • on the territory of any of the Parties in Europe or North America, on the Algerian Departments of France 2, on the territory of Turkey or on the Islands under the jurisdiction of any of the Parties in the North Atlantic area north of the Tropic of Cancer;
    • on the forces, vessels, or aircraft of any of the Parties, when in or over these territories or any other area in Europe in which occupation forces of any of the Parties were stationed on the date when the Treaty entered into force or the Mediterranean Sea or the North Atlantic area north of the Tropic of Cancer.”

    The principle of providing assistance

    With the invocation of Article 5, Allies can provide any form of assistance they deem necessary to respond to a situation. This is an individual obligation on each Ally and each Ally is responsible for determining what it deems necessary in the particular circumstances.

    This assistance is taken forward in concert with other Allies. It is not necessarily military and depends on the material resources of each country. It is therefore left to the judgment of each individual member country to determine how it will contribute. Each country will consult with the other members, bearing in mind that the ultimate aim is to “to restore and maintain the security of the North Atlantic area”.

    At the drafting of Article 5 in the late 1940s, there was consensus on the principle of mutual assistance, but fundamental disagreement on the modalities of implementing this commitment. The European participants wanted to ensure that the United States would automatically come to their assistance should one of the signatories come under attack; the United States did not want to make such a pledge and obtained that this be reflected in the wording of Article 5.

    1. Article 6 has been modified by Article 2 of the Protocol to the North Atlantic Treaty on the Accession of Greece and Türkiye.
    2. On January 16, 1963, the North Atlantic Council modified this Treaty in its decision C-R(63)2, point V, on the independence of the Algerian departments of France.
    3. Documents on Canadian External Relations, Vol. 15, Ch. IV.
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  • Invocation of Article 5

    The 9/11 terrorist attacks

    The United States was the object of brutal terrorist attacks on 11 September 2001. The Alliance's 1999 Strategic Concept had already identified terrorism as one of the risks affecting NATO’s security. The Alliance’s response to 9/11, however, saw NATO engage actively in the fight against terrorism, launch its first operations outside the Euro-Atlantic area and begin a far-reaching transformation of its capabilities. Moreover, it led NATO to invoke Article 5 of the Washington Treaty for the very first time in its history.

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    An act of solidarity

    On the evening of 12 September 2001, less than 24 hours after the attacks, the Allies invoked the principle of Article 5. Then NATO Secretary General Lord Robertson subsequently informed the Secretary-General of the United Nations of the Alliance's decision.

    The North Atlantic Council – NATO’s principal political decision-making body – agreed that if it determined that the attack was directed from abroad against the United States, it would be regarded as an action covered by Article 5. On 2 October, once the Council had been briefed on the results of investigations into the 9/11 attacks, it determined that they were regarded as an action covered by Article 5.

    By invoking Article 5, NATO members showed their solidarity toward the United States and condemned, in the strongest possible way, the terrorist attacks against the United States.

    Taking action

    After 9/11, there were consultations among the Allies and collective action was decided by the Council. The United States could also carry out independent actions, consistent with its rights and obligations under the United Nations Charter.

    On 4 October, once it had been determined that the attacks came from abroad, NATO agreed on a package of eight measures to support the United States. On the request of the United States, it launched its first ever anti-terror operation – Eagle Assist – from mid-October 2001 to mid-May 2002. It consisted in seven NATO AWACS radar aircraft that helped patrol the skies over the United States; in total 830 crew members from 13 NATO countries flew over 360 sorties. This was the first time that NATO military assets were deployed in support of an Article 5 operation.

    On 26 October, the Alliance launched its second counter-terrorism operation in response to the attacks on the United States, Active Endeavour. Elements of NATO's Standing Naval Forces were sent to patrol the Eastern Mediterranean and monitor shipping to detect and deter terrorist activity, including illegal trafficking. In March 2004, the operation was expanded to include the entire Mediterranean.

    The eight measures to support the United States, as agreed by NATO were:

    • to enhance intelligence-sharing and cooperation, both bilaterally and in appropriate NATO bodies, relating to the threats posed by terrorism and the actions to be taken against it;
    • to provide, individually or collectively, as appropriate and according to their capabilities, assistance to Allies and other countries which are or may be subject to increased terrorist threats as a result of their support for the campaign against terrorism;
    • to take necessary measures to provide increased security for facilities of the United States and other Allies on their territory;
    • to backfill selected Allied assets in NATO’s area of responsibility that are required to directly support operations against terrorism;
    • to provide blanket overflight clearances for the United States and other Allies’ aircraft, in accordance with the necessary air traffic arrangements and national procedures, for military flights related to operations against terrorism;
    • to provide access for the United States and other Allies to ports and airfields on the territory of NATO member countries for operations against terrorism, including for refuelling, in accordance with national procedures;
    • that the Alliance is ready to deploy elements of its Standing Naval Forces to the Eastern Mediterranean in order to provide a NATO presence and demonstrate resolve;
    • that the Alliance is similarly ready to deploy elements of its NATO Airborne Early Warning Force to support operations against terrorism.
  • Enhanced collective defence measures

    On the request of Türkiye, on three occasions, NATO has put collective defence measures in place: in 1991 with the deployment of Patriot missiles during the Gulf War, in 2003 with the agreement on a package of defensive measures and conduct of Operation Display Deterrence during the crisis in Iraq, and in 2012 in response to the situation in Syria with the deployment of Patriot missiles.

    Since Russia’s illegal annexation of Crimea in 2014 and the rise of security challenges from the south, including brutal attacks by ISIL and other terrorist groups across several continents, NATO has implemented the biggest increase in collective defence since the Cold War. For instance, it has tripled the size of the NATO Response Force (NRF), a highly ready and technologically advanced multinational force; established a 5,000-strong Spearhead Force within the NRF; and deployed multinational battlegroups in Estonia, Latvia, Lithuania and Poland. NATO has also increased its presence in the southeast of the Alliance, centred on a multinational brigade in Romania. The Alliance has further stepped up air policing over the Baltic and Black Sea areas and continues to develop key military capabilities, such as Joint Intelligence, Surveillance and Reconnaissance. At the Warsaw Summit in July 2016, Allies recognised cyber defence as a new operational domain, to enable better protection of networks, missions and operations; and at the meeting of foreign ministers in November 2019, Allies agreed to recognise space as a new operational domain to "allow NATO planners to make requests for Allies to provide capabilities and services, such as hours of satellite communications."

    Following Russia’s unprovoked invasion of Ukraine – which started in February 2022 – and in line with its defensive planning to protect all Allies, NATO is taking additional steps to further strengthen deterrence and defence across the Alliance. This includes the deployment of the NRF for the first time in a deterrence and defence role. Allies have placed thousands of additional forces at high readiness, ensuring that the NRF continues to have the speed, responsiveness and capability to defend NATO territory and populations. Moreover, at an extraordinary Summit on 24 March 2022, NATO Leaders agreed to significantly strengthen the Alliance’s longer-term deterrence and defence posture. This was followed by a united and firm commitment of Allies, at the Madrid Summit in June 2022, to concrete measures such as deploying additional in-place combat-ready forces on the eastern flank, to be scaled up from the existing battlegroups to brigade-size units where and when required, underpinned by rapidly available reinforcements, prepositioned equipment, and enhanced command and control. They also made initial offers to NATO’s new force model, which will strengthen and modernise the NATO Force Structure and will resource a new generation of military plans. All these steps, together with the release of the 2022 Strategic Concept, which identified Russia as “the most significant and direct threat to Allies’ security and to peace and stability in the Euro-Atlantic area” will substantially strengthen NATO’s deterrence and forward defences.

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  • Standing forces

    Collective defence measures are not solely event-driven. NATO has a number of standing forces on active duty that contribute to the Alliance’s collective defence efforts on a permanent basis. These include NATO’s standing maritime forces, which are ready to act when called upon. They perform different tasks ranging from exercises to operational missions, in peacetime and in periods of crisis and conflict.

    Additionally, NATO has an integrated air defence system to protect against air attacks, which also comprises the Alliance’s ballistic missile defence system. NATO also conducts several air policing missions, which are collective peacetime missions that enable NATO to detect, track and identify all violations and infringements of its airspace and to take appropriate action. As part of such missions, Allied fighter jets patrol the airspace of Allies who do not have fighter jets of their own. They run on a 24/7 basis, 365 days a year.

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What is an Article 5 collective Defence? ›

Collective defence means that an attack against one Ally is considered as an attack against all Allies. The principle of collective defence is enshrined in Article 5 of the Washington Treaty. NATO invoked Article 5 for the first time in its history after the 9/11 terrorist attacks against the United States.

What does Article 5 of NATO say? ›

Article 5 of the North Atlantic Treaty, NATO's founding document, says that any attack on a NATO member in Europe or North America “shall be considered an attack against them all.”

What happens if a NATO member attacks another NATO member? ›

The NATO Alliance consists of 30 member states from North America and Europe. 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.

Can a country be kicked out of NATO? ›

As of 2022, no member state has rescinded their membership, although it has been considered by several countries. Notwithstanding, a number of former dependencies of NATO members have never applied for membership subsequent to their becoming independent states.

Has NATO Article 5 been invoked? ›

Article 5 is the cornerstone of the North Atlantic Treaty Organization (NATO) and states that an attack on one member of NATO is an attack on all of its members. Despite its importance, NATO has only invoked Article 5 once in its history—in response to the terrorist attacks of September 11, 2001.

What is Article 5 Simplified? ›

Article 5: Amendments: The Constitution can be changed. New amendments can be added to the US Constitution with the approval by a two-thirds vote in each house of Congress (67, 281) and three-fourth vote by the states (38).

Why is Article 5 so important? ›

Realizing that over time the nation may want to make changes to the Constitution, Article V establishes the amendment process. But unlike laws and regulations, which can be passed or amended by a simple majority of those voting in Congress, the Constitution is difficult to change.

How many times has NATO Article 5 been triggered? ›

The organization's collective defense obligations, detailed in Article 5, have been invoked only once, on behalf of the United States after 9/11.

What is the main point of Article 5? ›

Article Five of the United States Constitution describes the process for altering the Constitution. Under Article Five, the process to alter the Constitution consists of proposing an amendment or amendments, and subsequent ratification.

Can NATO defend against Russia? ›

Fact: NATO ballistic missile defence is not directed against Russia and cannot undermine Russia's strategic deterrence capabilities. It is designed to protect European Allies against missile threats from outside the Euro-Atlantic area. The Aegis Ashore site in Romania is purely defensive.

Can two NATO countries fight? ›

The Treaty doesn't dedicate any explicit provisions regarding members attacking each other.” The goal of collective defence is codified in Article 5 NAT. It states that an attack against one member of NATO should be considered an attack against all.

Has NATO ever been attacked? ›

The 11 September attacks in the United States, a NATO member, invoked Article 5 of the North Atlantic Treaty. It remains the only time since NATO's inception that an attack from an external party or state has been deemed an attack on all NATO members.

When did Russia leave NATO? ›

The Russia–NATO relations started to deteriorate, following the Ukrainian Orange Revolution in 2004–05. In October 2021, following an incident in which NATO expelled eight Russian officials from its Brussels headquarters, Russia suspended its mission to NATO and ordered the closure of the NATO office in Moscow.

When did France leave NATO? ›

Did you know that France hosted NATO for 15 years? And that although it withdrew from NATO's military structure in 1966, it remained an Ally?

Why did France rejoin NATO? ›

When NATO began peacekeeping operations in the Balkans in the 1990s, French forces were active participants and France resumed its participation in the NATO Military Committee, because this body was making key decisions about peacekeeping operations.

What happens if a NATO state is attacked? ›

Article 5 of the treaty states that if an armed attack occurs against one of the member states, it shall be considered an attack against all members, and other members shall assist the attacked member, with armed forces if necessary.

How does Article 5 affect NATO countries? ›

Article 5 is the principle that an attack on one member of NATO is an attack on all members. It's been a cornerstone of the 30-member alliance since it was founded in 1949 as a counterweight to the Soviet Union. The principle aims to deter potential adversaries from attacking NATO members.

What happens if a NATO country attacks a non NATO country? ›

If a nation is attacked it can invoke article V of the NATO treaty, and the other 56 nations would have to come to its defence. However, if that nation is the aggressor and Started the war, then other NATO nations are not obligated to carry it on or participate.

What is an example of Article 5? ›

Article 5: No one shall be subjected to torture, or to cruel, inhuman or degrading treatment or punishment. administration believed the prohibitions against torture were “quaint” and “obsolete,” did not apply in what it labelled the “war on terrorism,” and even that the President could “override” international law.

What is an Article 5 violation? ›

Article 5: Ban on torture. No one shall be subjected to torture or to cruel, inhuman or degrading treatment or punishment.

Who triggered Article 5? ›

The triggering of Article 5 saw “NATO engage actively in the fight against terrorism, launch its first operations outside the Euro-Atlantic area and begin a far-reaching transformation of its capabilities”, according to the alliance.

How has Article 5 helped make the Constitution an enduring document? ›

It allows the Constitution to meet the needs of a changing society by ensuring basic rights, making necessary structural changes, extending government powers to meet specific needs, extending individual rights (voting) as society's views have changed on race, gender, and age.

What is the purpose of Article 5 of the Constitution quizlet? ›

What does Article 5 do? It is the amendment process. If Congress thinks it is necessary to change the Constitution, at least two-thirds of both the House of Representatives and the Senate have to propose an Amendment to the Constitution.

How many citizens are protected by NATO? ›

NATO is an alliance of 30 member states. In addition to the USA and Canada on the American continent, numerous European states are members. All member states together cover an area of 24.59 million km² and about 949.06 million people.

Is there an opposite of NATO? ›

The Warsaw Pact was the ideological opposite of NATO.

Does the EU have an Article 5 like NATO? ›

This, too, is somewhat similar to NATO. Article 5 states that any ally will "in exercise of the right of individual or collective self-defence" take "individually and in concert with other parties, such action as it deems necessary, including the use of armed force."

Is Article 5 an absolute right? ›

So - for example, if they've not properly assessed her needs or reviewed her detention as required by the law, they could be breaching article 5. Article 5 is a limited right.

How strong is NATO military? ›

The combined total of Nato military personnel currently exceeds 5.4 million – around four times as many as Russia, according to Statista. It has about five times as many aircraft, four times as many armoured vehicles and three times as many military ships.

Why is Ukraine not a member of NATO? ›

Plans for NATO membership were shelved by Ukraine following the 2010 presidential election in which Viktor Yanukovych, who preferred to keep the country non-aligned, was elected President.

Can NATO accept a country at war? ›

NATO's “open door policy” is based on Article 10 of its founding treaty. Any decision to invite a country to join the Alliance is taken by the North Atlantic Council on the basis of consensus among all Allies. No third country has a say in such deliberations.

Which country is stronger in NATO? ›

In 2022, the United States had the largest number of military personnel out of all North Atlantic Treaty Organization (NATO) countries, with 1.35 million troops.

Is Japan in NATO? ›

Japan, a key United States ally and not a NATO member, has delivered defensive supplies to Ukraine and imposed tough sanctions on Russia in tandem with the other Group of Seven (G7) countries.

Who controls NATO? ›

NATO's Command Structure is under the authority of the Military Committee, NATO's highest military authority composed of the Chiefs of Defence of all twenty-nine member countries. The NCS consists of two strategic commands: Allied Command Operations (ACO) and Allied Command Transformation (ACT).

Why is Israel not part of NATO? ›

A natural objection to Israeli membership in NATO is that it is situated 'outside' the North Atlantic region. This is beyond dispute. But it cannot be convincingly argued that Bulgaria or Turkey are “North Atlantic” states in any meaningful way either. The latter's frontiers extend well east of Israel's.

Do all NATO countries have to fight? ›

The Alliance is founded on the principle of collective defence, meaning that if one NATO Ally is attacked, then all NATO Allies are attacked. For example, when terrorists attacked the United States on 9/11 2001, all NATO Allies stood with America as though they had also been attacked.

How big is the NATO army? ›

around 3.5 million soldiers

Why did France leave NATO? ›

“France is determined to regain on her whole territory the full exercise of her sovereignty,” wrote French President Charles de Gaulle. The country intended to stop putting its military forces at NATO's disposal and intended to kick NATO military forces—and those of NATO members—off of its land.

Is China part of NATO? ›

For the first time, NATO members included China in the Strategic Concept as posing a “systemic challenge” to Euro-Atlantic security. NATO 2022 Strategic Concept, NATO, June 29, 2022.

Which countries are not NATO? ›

Which European nations are not in NATO?
  • Andorra.
  • Armenia.
  • Austria.
  • Azerbaijan.
  • Belarus.
  • Bosnia and Herzegovina.
  • Cyprus.
  • Finland.
29 Jun 2022

Why Sweden is not in NATO? ›

In 1949 Sweden chose not to join NATO and declared a security policy aiming for non-alignment in peace and neutrality in war. Sweden joined Partnership for Peace in 1994.

Can France rejoin NATO? ›

President Nicolas Sarkozy has announced that France will rejoin the North Atlantic Treaty Organization (NATO) 43 years after then-President Charles de Gaulle withdrew from the 26-nation military alliance.

Does Germany support NATO? ›

When the Federal Republic of Germany joined NATO on 6 May 1955, its membership eventually translated into a very substantial contribution to the Alliance's military strength in Europe.

Which French president pulled out of NATO? ›

Charles de Gaulle in 1966, when he took France out of NATO's integrated military command, where it remained until 2009.

Has Sweden and Finland joined NATO yet? ›

For decades, Sweden and Finland were content to work with NATO, but not become members of the defensive alliance.

Is France helping Ukraine? ›

That is why France, which is strongly committed to protecting heritage in conflict areas, is working alongside all of its European and international partners to safeguard Ukrainian heritage.

What does Article 5 of the UN mean? ›

1. States Parties recognize that all persons are equal before and under the law and are entitled without any discrimination to the equal protection and equal benefit of the law.

What is collective defense in the context of NATO? ›

Article 5 of the Washington Treaty provides the collective defense foundation for NATO's status as an alliance, stating that an attack on one shall be considered an attack on them all, and committing each member to respond to that attack.

Are NATO countries obligated to defend each other? ›

NATO is a defensive alliance whose members are committed to safeguarding the freedom and security of each other, against all threats, from all directions. Deterrence and defence is one of NATO's core tasks.

What does Article 5 give the power to do? ›

The Congress, whenever two thirds of both houses shall deem it necessary, shall propose amendments to this Constitution, or, on the application of the legislatures of two thirds of the several states, shall call a convention for proposing amendments, which, in either case, shall be valid to all intents and purposes, as ...

What does Article 5 provide for? ›

art. V ( The Congress, whenever two thirds of both Houses shall deem it necessary, shall propose Amendments to this Constitution, or, on the Application of the Legislatures of two thirds of the several States, shall call a Convention for proposing Amendments. . .. ).

Can NATO intervene in a war? ›

Under NATO's current treaty, if conflict occurs within the North Atlantic region, NATO will intervene for collective self-defense (North Atlantic Treaty Organization 2012).

Can NATO intervene militarily? ›

However, if diplomatic efforts fail, it has the military capacity to undertake crisis management operations alone or in cooperation with other countries and international organisations. NATO is a crisis management organisation that has the capacity to undertake a wide range of military operations and missions.

What is collective defense? ›

Collective Defense is the ability for organizations — comprising a sector, supply chain, or country — to share threat intelligence securely and in real time, providing all members an early warning system about potential incoming attacks.

Has NATO been used? ›

The treaty was created with an armed attack by the Soviet Union against Western Europe in mind, but the mutual self-defense clause was never invoked during the Cold War. Rather, it was invoked for the first and only time in 2001 during Operation Eagle Assist in response to the September 11 attacks.


1. Watch live: Reports Russian missiles have killed two people in NATO member Poland
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5. What is NATO's Article 5?
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