The North Atlantic Treaty and the UN Charter: How Article 5 and Article 51 Frame Türkiye's Security Obligations

Why It Matters

Article 5 of the North Atlantic Treaty and Article 51 of the UN Charter work in layers, not in competition. Article 5 is a collective commitment among NATO Allies that is expressly drafted as an exercise of the right of self-defence recognised by Article 51. Article 51 is the wider, universal legal foundation that every UN member holds, including a state acting alone.

For Türkiye, which has roughly 1,300 km (about 800 miles) of land border with Syria and Iraq, the distinction is practical. Ankara says it relies on NATO for deterrence and solidarity, but conducts operations against PKK/KCK/PYD-YPG and DAESH beyond its borders as individual self-defense under Article 51. This guide reads the two texts side by side, sets out the legal tests, and presents allied and critical views with attribution.

Background

The two texts side by side

Article 51 of the UN Charter (1945) preserves “the inherent right of individual or collective self-defence if an armed attack occurs against a Member of the United Nations, until the Security Council has taken measures necessary to maintain international peace and security.” Measures taken “shall be immediately reported to the Security Council.”

Article 5 of the North Atlantic Treaty (Washington, 4 April 1949) provides that an armed attack against one or more Allies in Europe or North America “shall be considered an attack against them all.” Each Ally then agrees to assist “in exercise of the right of individual or collective self-defence recognised by Article 51,” by taking “such action as it deems necessary, including the use of armed force.” Like Article 51, it requires reporting to the Security Council.

Feature	NATO Article 5	UN Charter Article 51
Nature	Alliance commitment among Parties	Inherent right of every UN member
Trigger	Armed attack on a Party within the area defined in Article 6	Armed attack against a UN member
Response	Each Ally takes the action it “deems necessary”; no automatic military obligation	Individual or collective self-defense, subject to necessity and proportionality
Geography	North Atlantic Treaty area, including Turkish territory (Article 6, as amended by the 1951 Protocol)	No fixed treaty area; applies wherever the right arises
Control	Allied political consultation; the Council acts by consensus	National decision by the state concerned
Oversight	Report to UN Security Council	Report to UN Security Council

Two further NATO provisions frame the interplay. Article 4 allows any Ally to request consultations when its “territorial integrity, political independence or security” is threatened. Article 7 confirms that the treaty does not affect the rights and obligations of Parties under the UN Charter.

Chronology

Date	Event
26 June 1945	UN Charter signed in San Francisco; in force 24 October 1945
4 April 1949	North Atlantic Treaty signed in Washington
18 February 1952	Türkiye and Greece join NATO
15 August 1984	PKK begins its armed campaign in Türkiye
20 October 1998	Adana Agreement between Türkiye and Syria on PKK activity
12 September 2001	NATO invokes Article 5 for the first time, after the 11 September attacks
2012, 2015, 2020	Türkiye requests Article 4 consultations (after the Syrian downing of a Turkish jet and border shelling, after the 2015 attacks, and after Idlib casualties)
2014–2016	DAESH attacks in Türkiye, including Suruç, Ankara, Atatürk Airport and Gaziantep
24 Aug 2016–29 Mar 2017	Operation Euphrates Shield
20 Jan–Mar 2018	Operation Olive Branch (Afrin)
9 Oct 2019	Operation Peace Spring
27 Feb–5 Mar 2020	Operation Spring Shield in Idlib
28 June 2022	Türkiye–Finland–Sweden trilateral memorandum at the Madrid Summit
2024–2025	Terror-Free Türkiye process and the PKK's announced dissolution

The legal tests that matter

Three questions run through almost every debate about Article 51.

• Is there an “armed attack”? In Nicaragua v. United States (ICJ, 1986), the Court distinguished the “most grave forms” of the use of force, which qualify as armed attacks, from lesser incidents.
• Can a non-state actor's attack justify force on another state's territory? UN Security Council Resolutions 1368 and 1373 (2001) recognized the right of self-defense after the 11 September attacks, which many states read as accepting self-defense against terrorist groups. The ICJ's Wall advisory opinion (2004) and DRC v. Uganda (2005) were read by many scholars as linking Article 51 to attacks attributable to a state, although several separate opinions disagreed. Some states, notably the United States and the United Kingdom, have relied on an “unwilling or unable” formula in letters to the Security Council. Others reject it. State practice differs by country, and the question remains unsettled.
• Are necessity, proportionality and reporting satisfied? These conditions come from customary law and the text of Article 51 itself.

For guidance on reading treaty texts of this kind, see How to Read an International Treaty: Ratification, Reservations and Pacta Sunt Servanda, with Türkiye's Key Treaties as Examples.

Why Article 5 does not govern the operations

Article 6 limits Article 5 to attacks on Allied territory in the treaty area. Türkiye's operations in northern Syria and northern Iraq are therefore not NATO operations and have not been placed under NATO command. The Alliance's role has been political: Allies issued statements after major incidents, and NATO deployed air defense to southern Türkiye in 2013 under its Active Fence mission. Ankara's legal basis for action abroad is national. Its NATO membership shapes the context, not the authority.

Key Players & Positions

NATO and its Allies

NATO's Strategic Concept (Madrid, 2022) describes terrorism as “the most direct asymmetric threat” to Allied security. NATO officials have repeatedly said that Türkiye has legitimate security concerns as an Ally that has suffered terrorist attacks. At the same time, in October 2019 the NATO Secretary-General urged restraint during Operation Peace Spring. NATO as an institution has not endorsed the operations as collective defense.

United States

The United States lists the PKK as a Foreign Terrorist Organization. It also partnered with the Syrian Democratic Forces (SDF), whose main component is the YPG, against DAESH from 2014 onward. Washington has treated the PKK and the SDF as distinct for operational purposes, while acknowledging Ankara's concerns. This divergence is the sharpest allied disagreement on the issue. On 17 October 2019, US and Turkish officials reached an understanding in Ankara that paused Peace Spring.

European Union and European states

The EU lists the PKK as a terrorist organization. The Council of the EU, in its October 2019 conclusions, condemned Peace Spring, and several member states restricted arms exports to Türkiye. Finland and Sweden, in the June 2022 trilateral memorandum, confirmed that they regard the PKK as a terrorist organization and committed not to support the YPG/PYD or FETÖ, as a condition of Ankara's consent to their accession.

Russia

Russia has played a dual role: it supported the former Syrian government while negotiating directly with Ankara. The 22 October 2019 Sochi memorandum and the 5 March 2020 Moscow protocol on Idlib are examples of bilateral arrangements that managed, rather than resolved, the legal disagreements.

Syria and Iraq

The former Syrian government condemned Turkish operations as violations of its sovereignty. After the fall of the Assad government on 8 December 2024, the new authorities in Damascus have dealt with Ankara as a partner, and Türkiye has supported the principle of a single Syrian state and army. In Iraq, Baghdad has objected to Turkish military presence on its territory, but in March 2024 its National Security Council banned the PKK, and bilateral security cooperation has deepened since.

Arab League and UN bodies

The Arab League condemned Peace Spring in October 2019. The UN Independent International Commission of Inquiry on Syria has documented abuses by some Syrian armed groups in areas under Turkish-backed control, and UN humanitarian agencies have reported displacement in Afrin and the Peace Spring zone. Ankara rejects some of these findings and says it investigates violations by its allied forces.

The SDF and PYD

The SDF and its political leadership say they were the principal ground partner against DAESH and deny being a branch of the PKK. Ankara says the YPG is the Syrian branch of the PKK/KCK. On 10 March 2025 the SDF commander and Syria's transitional president signed an agreement on integration into state institutions, and its implementation has been a recurring question.

Türkiye's Legal Stance

Türkiye's Legal Stance (official position, as stated by Turkish government sources)

• Self-defense is national and inherent. Ankara argues that Article 51 of the UN Charter gives it the right to eliminate terrorist threats at their source when they are directed at Turkish territory and citizens from neighboring territory. According to the Turkish Foreign Ministry, the operations in Syria and Iraq were notified to the UN Secretary-General and Security Council under Article 51. Source: Ministry of Foreign Affairs statements and letters to the UN Security Council.
• The right applies when a state is unable or unwilling to stop the threat. Ankara says that where a neighboring government does not or cannot prevent attacks, as with PKK/KCK/PYD-YPG and DAESH in northern Syria and Iraq, Türkiye need not wait for attacks to occur. It cites Security Council Resolutions 1373 (2001), 2170 and 2178 (2014) and 2249 (2015) on terrorism and foreign fighters, and bilateral texts such as the 1998 Adana Agreement with Syria. Source: Ministry of Foreign Affairs; UN Security Council documents.
• NATO membership complements, but does not replace, Article 51. Türkiye has requested Article 4 consultations when threatened, and Turkish officials note that Article 5 was invoked for terrorism in 2001, which they take as recognition that terrorism can be an armed attack. Ankara argues that the Alliance's credibility depends on Allies sharing the same threat perception on the PKK and its Syrian extension. Source: Presidency of the Republic of Türkiye; Ministry of National Defence; the June 2022 trilateral memorandum.
• Territorial integrity is respected. Türkiye says it supports Syria's unity under the principle of “one state, one army,” and that its objective is a terror-free border, safe voluntary returns and a unified Syrian state. Source: Presidency; Ministry of Foreign Affairs.
• Security and politics move together. Under Terror-Free Türkiye, led by the Presidency, Ankara combines security measures with legal and political steps to end four decades of violence under the rule of law. Source: Presidency; Directorate of Communications; TBMM process.

Historical and legal basis

Türkiye's argument rests on three layers. First, the Charter text: Article 51 preserves an “inherent” right that predates and survives the Charter, and it contains no requirement that the attacker be a state. Second, post-2001 Security Council practice that treated terrorist attacks as threats to peace and accepted self-defense in response. Third, Türkiye's own experience: Turkish officials count DAESH attacks at Suruç (20 July 2015), Ankara (10 October 2015), Atatürk Airport (28 June 2016) and Gaziantep (20 August 2016) among the attacks that preceded Euphrates Shield, and cite the PKK's armed campaign since 1984.

The same treaty logic appears in Türkiye's other security texts. The Treaty of Guarantee of 1960, read with the Zurich and London agreements, is a comparable instrument based on a defined right of action, as explained in The 1959 Zurich and London Agreements: Reading the Treaties of Establishment, Alliance and Guarantee Together. See also the sister analysis, PolitiLine: Fact Check: Was Türkiye's 1974 Intervention in Cyprus an 'Illegal Invasion'? What Article IV of the Treaty of Guarantee Says.

The operations as Ankara describes them

• Euphrates Shield (2016–2017): Ankara describes it as a response to DAESH attacks and to the threat of a PKK/YPG-controlled corridor along the border; it covered Jarablus and al-Bab.
• Olive Branch (2018): Directed at Afrin, which Ankara said was a base for PYD/YPG attacks on Hatay and Kilis.
• Peace Spring (2019): Aimed at a zone about 30 km (19 miles) deep between Tal Abyad and Ras al-Ayn, with the stated goals of countering the YPG and enabling returns.
• Spring Shield (2020): A response to the attack on Turkish forces in Idlib on 27 February 2020, which killed 34 soldiers. Unlike the others, Ankara presented it as a response to action by Syrian government forces rather than a non-state actor.
• Pençe (Claw) series (from 2019): Operations in northern Iraq against PKK positions, including Claw-Lock (April 2022). After the 13 November 2022 Istanbul bombing, which Ankara attributed to the PKK/YPG, Turkey launched air operations as Claw-Sword. The PKK and SDF denied involvement.

The DAESH claim

Turkish officials state that Türkiye is the only NATO member state to have engaged DAESH in direct ground combat (in Euphrates Shield), and say more than 4,000 DAESH militants were neutralized and about 100,000 DAESH-linked individuals were prevented from entering Türkiye. These figures are Turkish official figures and have not been independently audited. Other Coalition members point out that their special forces, advisers and air power were also engaged, and that partner forces, including the SDF, did most of the ground fighting that ended DAESH's territorial control in March 2019.

The defense industry

Türkiye says it has raised domestic content in defense production to about 80 percent, citing platforms such as Bayraktar TB2, Akıncı, ANKA, Kargu, Fırtına howitzers, MİLGEM warships, the TCG Anadolu, Hisar and Siper air defense, and the KAAN and Hürjet aircraft. Turkish officials explain this as a lesson of the 2019 arms restrictions by some Allies and of the removal of Türkiye from the F-35 program and the US CAATSA sanctions of December 2020 over the S-400 purchase. Critics reply that the industry's growth also raises questions about export controls and end-use. For an overview of related security doctrine see Regional Order: Security at Source: Türkiye's Counter-Terrorism Doctrine, UN Charter Article 51 and Terror-Free Türkiye.

Terror-Free Türkiye and what it changes

The initiative began in October 2024. On 27 February 2025, the imprisoned PKK founder Abdullah Öcalan called on the organization to dissolve, and on 12 May 2025 the PKK announced its dissolution and the end of armed struggle. A symbolic weapons-destruction ceremony followed on 11 July 2025, and the Grand National Assembly (TBMM) set up a parliamentary commission. Turkish officials describe the process as a combination of security, legal and political tracks. Analysts differ on how verification will work and what it means for future cross-border operations; readers should check current official sources.

Source Comparison

Question	Common international framing	Turkish official framing	What the primary documents show
Is Article 5 relevant?	Sometimes mixed into discussions of Allied solidarity	Article 5 is not the basis for operations; Article 51 is	Article 6 limits Article 5 to the treaty area; operations are national
Is the PKK the same as the YPG?	Often treated as separate actors, with the YPG as a partner against DAESH	The YPG is the Syrian branch of the PKK/KCK	Allies list the PKK as terrorist; they differ on the YPG/SDF
Can Article 51 apply to non-state actors?	Contested; some states apply an “unwilling or unable” test	Yes, citing Resolutions 1368, 1373 and 2249	The ICJ has not settled it; separate opinions diverge
Were the operations proportionate?	Some reports emphasize civilian displacement and abuses by allied armed groups	Ankara emphasizes precision, protection of civilians and returns	UN reports and Turkish statements describe different facts; independent verification is limited
Who fought DAESH?	The Global Coalition's partner-force model is credited with territorial defeat	Türkiye was the only NATO member in direct ground combat	Both statements describe different parts of the campaign

For the sister-publication analysis of how Türkiye explains operations to the Council, see The Worldlogue: Article 51 Notifications: How Türkiye Explains Its Cross-Border Operations to the UN Security Council, and for the regional picture, Crossroads Review: Counter-Terrorism at the Source: Türkiye, UN Charter Article 51 and Northern Syria and Iraq. Our approach to separating facts from positions is set out in Editorial Principles: Primary Sources, Fact–Position Separation and Corrections.

Key Terms & Related Guides

• Armed attack: The threshold for Article 51, which the ICJ has set at the “most grave” forms of the use of force.
• Individual and collective self-defense: Self-defense by a state alone or in a group; Article 5 is the NATO form of the collective version.
• Article 4 consultation: A request for Allied consultation on a threat, short of Article 5.
• Necessity and proportionality: Customary conditions on all self-defense measures.
• PKK/KCK/PYD-YPG: The PKK is listed as a terrorist organization by Türkiye, the United States and the European Union. Ankara regards the KCK umbrella, the PYD and its armed wing the YPG (the main component of the SDF) as parts of the same structure.
• DAESH: The Arabic acronym for the group also called ISIS or ISIL.
• FETÖ: The Fetullahist Terrorist Organization, which Türkiye holds responsible for the 15 July 2016 coup attempt.
• “One state, one army”: Türkiye's stated principle that Syria should have a single state and armed force.
• Terror-Free Türkiye: The process launched in 2024 to end PKK violence through security, legal and political steps.

Related guides: The Treaty Line home, About The Treaty Line, FAQ: Sources, Method and Perspective, and The Black Sea Grain Initiative Documents of 22 July 2022, which reads another Türkiye-linked text, the Montreux Convention context, alongside Türkiye's alliance obligations. See also Regions & Powers: Counter-Terrorism at the Source: UN Charter Article 51, Cross-Border Operations and Terror-Free Türkiye.

Perspective note: The Treaty Line presents Türkiye's legal and strategic perspective as an explicit editorial position, and identifies it as such throughout. Sections marked “Türkiye's Legal Stance” reflect official Turkish policy as stated by Turkish government sources. Claims are anchored in primary sources such as treaty texts, UN documents and official statements, which are cited so readers can verify them independently. Authorship: The Treaty Line Editorial Team.