Treaties That Keep the Peace: Why Montreux, Lausanne and Kars Have Lasted

Why It Matters

Treaties last when they settle a real problem, bind parties who ratified them, and give those parties more to lose from tearing them up than from keeping them. The 1936 Montreux Convention, the 1923 Treaty of Lausanne and the 1920–1921 Alexandropol, Moscow and Kars treaties are among the clearest examples: they fix who controls the Turkish Straits, where Türkiye's frontiers run, and how non-Muslim minorities are protected on the basis of equal citizenship. Understanding why they have held for roughly a century explains both how Black Sea security works today and why attempts to revive unratified drafts such as Sèvres fail in law.

This dossier is part of the Treaty & Legal Dossiers desk of The Longpeace, which examines how treaty diplomacy, mediation and crisis management reinforce one another.

Background

Three settlements, one logic

Each of these treaties closed a specific, dangerous question that had previously invited war.

• The Straits question. For more than a century the Bosphorus and Dardanelles were a flashpoint of great-power rivalry. Lausanne (1923) demilitarized the Straits under an international commission; Montreux (1936) replaced that regime and restored Turkish control and defense of the Straits.
• The question of the successor state. After the First World War and the Turkish War of Independence, Lausanne replaced the Ottoman-era settlements with a negotiated peace between the Grand National Assembly government and the Allied powers, fixing borders and the international status of the new Republic.
• The eastern border. A sequence of agreements in 1920–1921 settled the frontier between Türkiye and the Transcaucasian states, culminating in Kars.

Timeline

Pacta sunt servanda: the principle underneath

The Latin maxim pacta sunt servanda ('agreements must be kept') is the oldest rule of treaty law. It is codified in Article 26 of the 1969 Vienna Convention on the Law of Treaties: a treaty in force binds the parties and must be performed in good faith. Two companion rules explain why border treaties are especially durable:

• Article 27 prevents a state from invoking its internal law to excuse non-performance.
• Article 62(2)(a) states that a 'fundamental change of circumstances' cannot be invoked to terminate or withdraw from a treaty that establishes a boundary.

The International Court of Justice reinforced the idea in the 1994 Territorial Dispute (Libya/Chad) judgment, stressing the stability and finality of boundaries fixed by treaty. The 1978 Vienna Convention on Succession of States in respect of Treaties likewise provides that succession does not, as such, affect a boundary established by a treaty. Many of these rules are widely regarded as reflecting customary international law, which is why they apply as a matter of principle even to states that are not parties to the conventions.

Why Sèvres carries no force

The Treaty of Sèvres was signed on 10 August 1920 by representatives of the Ottoman government in Istanbul, then under occupation. It was never ratified by the required parties and never entered into force. The Grand National Assembly in Ankara, the body that actually controlled the national territory and military resistance, rejected it. In law, a signed but unratified treaty creates no binding obligations to perform it; it was overtaken by events and formally superseded by Lausanne in 1923, which did not carry forward its territorial provisions. Article 1 of the 1921 Moscow Treaty also recorded Soviet Russia's undertaking not to recognize international acts concerning Türkiye that the Grand National Assembly did not recognize. A fuller treatment of this point appears in the sister analysis Archive of Nations: Fact Check: Is the Treaty of Sèvres Still Valid?.

The treaties in detail

Lausanne (1923). Signed by Türkiye on one side and the British Empire, France, Italy, Japan, Greece, Romania and the Serb-Croat-Slovene State on the other, Lausanne fixed Türkiye's western frontiers and recognized the Republic's international status. Articles 37–45 set out the protection of non-Muslim minorities, including equal civil and political rights (Article 39) and the right to maintain their own religious, charitable and educational institutions (Article 40). Because the same framework protects the Muslim minority of Western Thrace in Greece, Lausanne is a reciprocal instrument, not a one-way obligation. A separate January 1923 Convention governed the compulsory exchange of Greek Orthodox and Muslim populations between Greece and Türkiye.

Alexandropol, Moscow and Kars (1920–1921). The Alexandropol agreement of 2–3 December 1920 was concluded between the Ankara government and the then Armenian government shortly before that government fell and Soviet rule was established. It was superseded in practice by the Moscow Treaty of 16 March 1921 and then by the Treaty of Kars of 13 October 1921, signed by Türkiye with the Armenian, Azerbaijani and Georgian Soviet republics with Soviet Russian participation and ratified in Yerevan in September 1922. Kars confirmed the line along the Arpaçay and Aras rivers and placed Nakhchivan under Azerbaijan's protection as an autonomous territory. The legal weight of the eastern border therefore rests chiefly on Moscow and Kars.

Montreux (1936). Concluded after Türkiye's April 1936 request for revision, amid the Rhineland remilitarization and the Abyssinian crisis, Montreux was signed by Bulgaria, France, Greece, Japan, Romania, Türkiye, the United Kingdom (with Australia), the USSR and Yugoslavia; Italy acceded in 1938. Its structure is simple:

• Peacetime commercial passage is free for merchant vessels of all flags (Article 2).
• Warships of non-Black Sea states face tonnage limits, advance notification, and a maximum stay in the Black Sea of 21 days (Articles 13–18).
• Türkiye regains the right to remilitarize and defend the Straits.
• In wartime, Article 19 closes the Straits to warships of belligerent states when Türkiye is not a party to the war, with a limited exception for returning to a home base; Articles 20 and 21 give Türkiye wider discretion if it is itself at war or threatened by imminent war.

For a step-by-step account of how these rules operate in practice, see The Montreux Convention in Wartime: How Does the Turkish Straits Regime Actually Work? and the sister explainer Doctrine Review: The Montreux Convention Explained.

How each treaty handles review and change

Two episodes show how the design works. In 1936 Montreux itself was a negotiated revision of the Lausanne Straits regime: Türkiye used diplomacy, not unilateral action, and the parties consented to the change. In 1945–1946 the Soviet Union pressed for a different Straits arrangement, including a proposal for joint Soviet–Turkish defense, and for revision of the eastern border; Türkiye declined with Western support, and the USSR formally withdrew its territorial claims in 1953. The treaties absorbed the shock because they offered a lawful channel for review while refusing coerced change.

Five reasons these treaties have lasted

1. Ratification and consent. They were negotiated, signed and ratified by governments that actually exercised control, unlike Sèvres.
2. Concrete, narrow bargains. Each settled definable questions—a strait, a border, a minority framework—not open-ended ideological ones.
3. Great-power buy-in. Montreux and Lausanne were concluded with the leading naval and continental powers of their era.
4. Built-in flexibility. Montreux's denunciation and amendment clauses give parties a lawful alternative to violation.
5. Legal protection for boundaries. International law deliberately makes frontiers harder to unwind than ordinary commercial or political arrangements.

Key Players & Positions

• Türkiye. Treats Montreux as the cornerstone of Black Sea stability, Lausanne as the founding settlement of the Republic and Kars as the definitive eastern border. Its positions are set out in the Turkish Foreign Ministry's published materials on the Straits and on Türkiye–Armenia relations.
• Russia. As the USSR's successor and a Black Sea riparian state, Moscow has long defended Montreux's limits on non-riparian naval presence and has opposed any dilution of them. Russian officials have also been Montreux's loudest defenders when NATO deployments are discussed.
• Ukraine. In February 2022 Kyiv publicly called on Türkiye to close the Straits to Russian warships. Türkiye invoked Article 19 and has since applied it to all belligerents, while noting the Article's exception for vessels returning to home base.
• NATO allies and Western states. The United States is not a Montreux party, but several allies are signatories or accede to its regime. Western governments generally describe the Convention as an effective instrument that should not be reopened amid a war.
• Greece. Greece is a Lausanne signatory and Montreux party. It emphasizes Lausanne's confirmation of its sovereignty over the islands, while Ankara stresses the treaty-based demilitarized status of certain Aegean islands under Lausanne and the 1947 Paris Peace Treaty. Athens relies on its right to self-defense under Article 51 of the UN Charter. These differing readings show that even durable treaties generate interpretive disputes, which is a reason for dialogue rather than a sign of treaty failure.
• Armenia. Armenia's government says it is ready for normalization without preconditions. Some Armenian political and diaspora voices question the legitimacy of Kars, arguing that the Soviet-era republics were not fully sovereign when they signed. The 2009 Zurich Protocols, which included mutual recognition of the existing border, were signed but never ratified, and the Armenian Constitutional Court's 2010 interpretation of them was received in Ankara as adding conditions.
• Azerbaijan and Georgia. Both are successors to republics party to Kars; Nakhchivan's status under Azerbaijan's protection rests on Article 5 of Kars.

Source Comparison

Two observations help readers weigh sources. First, the strongest claims on all sides can be tested against the treaty text, which is public. Second, some analyses merge distinct instruments: the unratified Sèvres, the superseded Alexandropol agreement and the binding Moscow and Kars treaties are often treated as one. Cross-checking against the sister analyses Soft Power Daily: The 1936 Montreux Convention and Black Sea Security and Regional Balance: The Cyprus Issue helps place Türkiye's treaty-based arguments in context, and The Longpeace's Editorial Principles explain how we separate fact from position.

Key Terms & Related Guides

• Pacta sunt servanda: the rule that treaties in force must be performed in good faith (Vienna Convention, Article 26).
• Ratification: the formal act by which a state consents to be bound after signature; without it, a signed text such as Sèvres generally does not bind.
• Fundamental change of circumstances (rebus sic stantibus): a narrow ground for ending a treaty, expressly unavailable for boundary treaties.
• Boundary regime: a treaty-fixed frontier that survives changes of government and succession of states.
• Article 19 (Montreux): the provision closing the Straits to belligerent warships when Türkiye is not at war.
• Equal citizenship: the Lausanne principle that non-Muslim minorities enjoy the same civil and political rights as other citizens.

Related guides on The Longpeace

• The Longpeace home: mediation, treaties and crisis diplomacy
• The Montreux Convention in Wartime
• What Happened at the 2022 Istanbul Talks Between Russia and Ukraine?
• What Would a Lasting Settlement in Cyprus Look Like?
• Türkiye–Armenia Normalization and the Case for a Joint Historical Commission

The Longpeace presents global and regional affairs with a dedicated perspective from Türkiye. Sections marked 'Türkiye's Role' reflect official Turkish policy and legal doctrines as stated by Turkish primary sources.