The North Atlantic Treaty — commonly referred to as the NATO Treaty or the Washington Treaty — is the foundation upon which the world’s most powerful military alliance rests. Concluded on 4 April 1949 in Washington D.C., the Treaty continues to this day to form the legal and political backbone of the North Atlantic Treaty Organization (NATO). With 32 member states and a Secretary General in the person of the Dutchman Mark Rutte, the Alliance is once again at the centre of international attention.
In this article we analyse the Treaty from a legal perspective: its content and structure, the procedures for accession and withdrawal, the mechanisms for dispute settlement, and the most relevant developments of recent decades. We focus specifically on the legal dimensions that matter to lawyers, law students, policymakers and interested citizens.
1. Content and legal structure of the NATO Treaty
The North Atlantic Treaty is a classic multilateral treaty under public international law. It contains fourteen articles and was deliberately kept concise: its founders wanted a flexible instrument that leaves political room for sovereign member states.
Article 5: the cornerstone of collective defence
The most cited — and most debated — article is undoubtedly Article 5. This article provides that an armed attack against one or more member states shall be considered an attack against all. Each member state undertakes to assist the attacked state, “including the use of armed force.”
What many people do not realise is that Article 5 does not contain an automatic obligation to undertake military intervention. The provision states that each member state shall take “such action as it deems necessary, including the use of armed force.” The nature of the assistance thus remains a national decision. This has in practice given rise to considerable legal and political debate about the scope of the allied obligation.
Article 5 has been formally invoked only once: following the attacks of 11 September 2001 on the United States. This led to the ISAF mission in Afghanistan, in which the Netherlands participated for many years.
Article 4: consultation in the event of a threat
Article 4 gives member states the right to request consultations whenever their territorial integrity, political independence or security is threatened. This article is less binding than Article 5, but serves as an essential diplomatic safety valve. In practice it has been invoked on several occasions, including by Turkey during tensions on the Syrian border and by the Baltic states following Russian aggression in Ukraine.
Other key provisions
The remaining articles concern the promotion of peace and stability (arts. 1–2), cooperation on defence matters (art. 3), the institutional structure of NATO (art. 9), the accession of new members (art. 10), the relationship with the UN Charter (art. 7), and the withdrawal of member states (art. 13).
Particularly relevant is Article 7, which explicitly governs the relationship with the UN Charter: the NATO Treaty leaves intact the rights and obligations of member states under the UN Charter. This means that the UN Charter is hierarchically superior to the NATO Treaty. In theory, NATO decisions may therefore conflict with UN obligations — a tension that manifested itself in practice during the NATO operation in Kosovo (1999), which took place without an explicit UN Security Council mandate.
2. NATO as an international organisation: legal status
NATO is an international organisation with legal personality. This is legally significant because NATO as such can conclude contracts, appear before courts and enjoys immunities. The legal status of NATO headquarters and personnel is further elaborated in the Paris Protocol (1952) and the NATO Status of Forces Agreement (SOFA, 1951).
The SOFA regulates, among other things, the legal position of troops of one member state on the territory of another. The sending state retains jurisdiction over its forces for service offences; the receiving state has jurisdiction over criminal offences committed off duty. For civil damage a special arrangement applies: the receiving state handles claims and subsequently divides the costs (generally 75/25) with the sending state.
In the Netherlands this arrangement has been further elaborated in the Act on Compensation for Damage Caused by NATO Motor Vehicles, which gives citizens who suffer damage caused by NATO vehicles a direct claim against the Dutch State.
3. Accession to NATO: procedure and recent developments
The legal procedure
Article 10 of the NATO Treaty governs accession. The article provides that member states may unanimously invite any European state that is able and willing to fulfil the obligations of the Treaty to accede. Following acceptance of the invitation, the candidate member signs the Treaty and deposits the instrument of accession with the government of the United States, which acts as depositary.
The accession procedure in practice proceeds as follows:
- The candidate country formally submits a request to NATO.
- The NATO Council assesses whether the country meets the political criteria (democracy, rule of law, human rights) and the military and financial obligations.
- If the Council unanimously agrees, an invitation to begin accession talks is extended.
- After the conclusion of accession talks, the candidate country signs an accession protocol.
- All existing member states ratify the protocol in accordance with their national constitutional procedures.
- After deposit of the instrument of ratification with the United States, membership takes effect.
The unanimity requirement makes accession vulnerable to political blockades. A single member state can delay or even block the process. This manifested itself in recent practice with the accession of Finland and Sweden.
Finland and Sweden: a legal case study
Following the Russian invasion of Ukraine in February 2022, Finland and Sweden submitted their accession requests in May 2022. Turkey initially blocked ratification, arguing that both countries harboured members of the PKK (an organisation designated as terrorist by Turkey) and supporters of the Gülen movement.
After diplomatic negotiations — and the conclusion of a trilateral agreement — Turkey gave its consent. Finland acceded in April 2023 as the 31st member. Sweden followed in March 2024 as the 32nd member, after Hungary had also granted its parliamentary approval.
From a legal perspective it is noteworthy that the Treaty contains no procedure for the situation where a member state links its approval to conditions that lie outside the Treaty. The entire process was conducted through diplomatic negotiations, not through a legally enforceable mechanism.
The open-door policy and its limits
NATO officially maintains an “open-door policy” based on Article 10. In practice, however, there are considerable political and factual limits. Georgia and Ukraine were told in 2008 that they would “eventually” become members, but were not offered a Membership Action Plan (MAP). This proved a controversial decision over which NATO members were internally divided.
Legally, the open-door policy is a political commitment, not a legally enforceable right. A candidate state has no legal means to compel accession if the unanimity requirement is not fulfilled.
4. Withdrawal from NATO: procedure and implications
The legal procedure
Article 13 of the NATO Treaty governs withdrawal. The article is remarkably simple: a member state that wishes to cease to be a party after twenty years may do so by depositing an instrument of denunciation with the government of the United States. Withdrawal takes effect one year after notification.
No formalities are required other than the formal notification. The Treaty imposes no substantive conditions on withdrawal. No sanction or procedure before the NATO Council is required. This was a deliberate choice by the Treaty’s drafters: it had to be straightforward to leave, so that member states would not feel trapped.
Historical precedent: the French case
France withdrew from NATO’s integrated military command structure in 1966 under President de Gaulle. This was not, however, a withdrawal from the Treaty itself (Article 13), but a withdrawal from military integration. France remained a formal member of the political alliance. It was not until 2009, under President Sarkozy, that France fully returned to the military structure.
Current affairs: Article 13 in the political debate
Article 13 has once again been prominent in political debate in recent years. In the context of Donald Trump’s second term as US President, the question was raised in political and legal circles whether the United States could denounce the Treaty without the consent of Congress. Constitutional law scholars were divided: the Treaty was ratified by the Senate, but the denunciation procedure is not explicitly governed by the US Constitution. This debate is relevant for all NATO partners, as the United States contributes by far the largest military and financial share.
5. Decision-making within NATO: the consensus principle
The NATO Council decides exclusively on the basis of unanimity. There is no vote; tacit agreement counts as consensus. This has far-reaching legal and practical consequences.
Each member state effectively holds a veto. This explains why NATO decisions sometimes take a long time to reach and why communiqués and statements sometimes contain diplomatically vague formulations that mask internal divisions. The NATO Summit in The Hague in June 2025 provided a topical example: the final text on support for Ukraine was formulated in such a way that both northern and southern allies could agree to it.
From a legal perspective the consensus principle carries profound significance: NATO decisions are politically binding on the member states that agree to them, but are not legally enforceable through an external judicial body. No sanctions exist for non-compliance.
6. Dispute settlement within NATO
The absence of a formal mechanism
A striking feature of the NATO Treaty is the absence of a formal dispute settlement mechanism for disputes between member states concerning the interpretation or application of the Treaty. The SOFA provides in Article XVI that disputes shall be resolved through negotiation or through the NATO Council; referral to external courts is not envisaged.
In practice, political and strategic disputes are resolved through diplomacy. Formal legal proceedings are rare and are confined to contractual and financial matters.
Relevant case law
CJEU C-186/19 (Supreme/NATO states): In this case a fuel supplier claimed payment from a number of NATO member states for fuel supplied during the ISAF mission in Afghanistan. The Court of Justice of the EU held that the Paris Protocol allows NATO headquarters to be parties to national proceedings. The internal NATO procedure (an escrow mechanism) served as a first step, but did not preclude judicial review.
ECLI:NL:RBDHA:2025:9705 (Supreme/NATO member states, The Hague): In this most recent version of the Supreme case, decided by the District Court of The Hague in 2025, the court held that it had jurisdiction to hear the supplier’s civil claim. The internal NATO procedure had been exhausted, but was not binding on the member states that were not party to the escrow agreement. This judgment is a clear illustration of the limits of NATO immunity in commercial transactions.
ECLI:NL:HR:2021:1956 (Supreme Court of the Netherlands): The Supreme Court confirmed that NATO entities enjoy functional immunity for acts connected with their military tasks. For commercial transactions no such immunity applies, and national courts have jurisdiction.
ECLI:NL:RBLIM:2017:1002: The District Court of Limburg held that immunity may yield where the internal NATO procedure does not provide a genuine alternative to a fair trial. This engages the right of access to a court as enshrined in Article 6 ECHR.
Disputes concerning national implementation
At the national level, Dutch courts review only marginally whether the government is fulfilling its international obligations, including NATO obligations. The courts exercise restraint in matters of foreign and defence policy, given the government’s broad discretion (ECLI:NL:PHR:2024:1279). Only in cases of clear violation of well-defined legal norms or manifest unlawfulness may the courts intervene.
7. National democratic oversight of NATO obligations
Parliamentary approval
In the Netherlands, ratification of the NATO Treaty and accession protocols requires parliamentary approval pursuant to Article 91 of the Constitution. Parliament can technically block the accession of a new member by refusing ratification. In practice this has not occurred with NATO enlargements, but the instrument exists.
Direct effect of NATO decisions
Once a treaty has been approved and published, it has binding force in the Dutch legal order (art. 93 of the Constitution). In the event of a conflict, the international legal decision takes precedence over national legislation (art. 94 of the Constitution). This means that a NATO decision that is “binding on all persons” in principle has direct effect and can set aside national legislation.
Judicial review
Dutch courts do not review legislation against the Constitution (art. 120 of the Constitution), but do review against treaty law and human rights treaties. In cases of conflict between NATO obligations and fundamental rights (such as the right to a fair trial) the courts may intervene, but this is exceptional.
8. Liability for damage caused by NATO operations
Liability for damage caused by NATO operations on the territory of a member state is primarily governed by Article VIII of the NATO Status of Forces Agreement. The system works as follows:
For damage to third parties (civilians) caused by NATO troops on Dutch territory, the Dutch State acts as the primary point of contact. The State compensates the damage and subsequently recovers the costs from the sending state on the basis of a standard ratio of 75% (sending state) to 25% (receiving state). Where damage occurs off duty or through intent or gross negligence, the individual servicemember or the sending state may be directly liable.
For damage caused by NATO motor vehicles in the Netherlands a separate Act applies: the Act on Compensation for Damage Caused by NATO Motor Vehicles, which gives the injured party a direct claim against the Dutch State.
9. Current developments: NATO in 2025–2026
The rearmament debate and the 5% target
At the NATO Summit in The Hague in June 2025, intensive discussions took place on defence spending. The United States, under President Trump, pressed for a target of 5% of GDP, well above the existing 2% benchmark. Legally speaking, the 2% norm is not a hard legal obligation but a political commitment. Non-compliance leads to diplomatic pressure, but not to formal sanctions.
Secretary General Rutte played a crucial role in forging consensus around a new formulation that gave member states sufficient flexibility. The final communiqué contained a target date and a trajectory, but no binding percentage.
Ukraine and the membership perspective
The question of a possible NATO membership for Ukraine dominates the Alliance’s agenda. Article 10 requires a European state capable of fulfilling the principles of the Treaty — Ukraine meets the geographical and political conditions, but the active armed conflict on its territory constitutes a factual and political obstacle. The collective defence obligation of Article 5 would be activated immediately upon accession during an ongoing conflict.
Legally the situation is complex: the Treaty contains no explicit exclusion of countries at war, but the unanimity requirement makes accession during an ongoing conflict politically near-impossible as long as not all member states agree.
Hybrid threats and the scope of Article 5
A growing debate concerns the question of whether cyberattacks, disinformation campaigns and sabotage of infrastructure can qualify as an “armed attack” within the meaning of Article 5. NATO formally acknowledged in 2016 that cyberattacks can trigger Article 5, but a legally binding definition is lacking. This creates legal uncertainty.
10. Critical assessment: the limits of the Alliance
The NATO Treaty is a legal instrument of great force, but it also has inherent weaknesses. The absence of a binding dispute settlement mechanism, the exclusive reliance on unanimity, and the non-enforceability of defence spending targets are structural shortcomings from a rule-of-law perspective.
Moreover, the tension between national sovereignty and allied obligations is growing. Member states can in practice interpret their Article 5 obligations as they see fit, without legal consequences for a minimalist interpretation. This is inherent to the intergovernmental structure of NATO — but it raises serious questions about the credibility of the collective defence guarantee in an era of increasing geopolitical tension.
Frequently asked questions (FAQ)
What exactly is Article 5 of the NATO Treaty? Article 5 provides that an armed attack against a member state shall be considered an attack against all. Each member state is then obliged to provide assistance, but determines the nature and extent of that assistance itself. The article has been invoked only once, following the attacks of 11 September 2001.
How does a country join NATO? Accession requires a unanimous decision by all current member states (art. 10), followed by signature and ratification by the acceding country and all existing members. The procedure can take months to years, depending on political circumstances.
Can a member state leave NATO? Yes. Under Article 13 a member state may withdraw by giving formal notice to the United States as depositary. Withdrawal takes effect one year later. There are no substantive conditions or sanctions attached to withdrawal.
Are NATO decisions legally enforceable? No. NATO decisions are politically binding but legally unenforceable. NATO has no supranational powers and cannot impose sanctions on member states that fail to implement decisions.
What is the legal status of the 2% defence spending target? The 2% target is a political commitment, not a hard legal obligation. Non-compliance leads to diplomatic pressure and reputational damage, but not to formal legal consequences.
Does NATO enjoy immunity from civil claims? Partially. NATO bodies enjoy functional immunity for acts connected with their military tasks. For commercial transactions no immunity applies and national courts have jurisdiction (ECLI:NL:HR:2021:1956).
Can courts intervene in the implementation of NATO policy? Dutch courts review foreign and defence policy only marginally. Only in cases of evident violation of clearly defined legal norms or fundamental rights may the courts intervene.
Can Ukraine join NATO? Legally, Article 10 poses no barrier — Ukraine is a European state that subscribes to the Treaty principles. Politically, accession during an ongoing armed conflict is near-impossible because unanimity among all 32 member states is required.
What is the NATO Status of Forces Agreement (SOFA)? The SOFA governs the legal position of troops of one member state on the territory of another, including jurisdiction over criminal offences and liability for civil damage.
What is the Netherlands’ role in disputes concerning NATO liability? The Netherlands has specific legislation for damage caused by NATO motor vehicles. For other damage claims the Dutch State acts as the primary point of contact; it subsequently recovers part of the costs from the sending state.
