The Turkish Straits as a Line of Power: Montreux, Black Sea Balance and Mediation

Why It Matters

The Turkish Straits (the Bosphorus, the Sea of Marmara and the Dardanelles) are the only sea exit from the Black Sea, and the 1936 Montreux Convention is the treaty that decides which ships may use them, how many, and under what wartime conditions. It pairs near-total freedom for commercial shipping with strict limits on non-littoral warships, and for ninety years this has kept the Black Sea from becoming an open arena for outside navies.

Since February 2022 that legal line has been tested by the Russia–Ukraine war. Türkiye's application of Article 19, together with the grain and prisoner diplomacy hosted in Istanbul and Antalya, explains why this treaty sits at the centre of European and Eurasian security debate. This pillar guide sets out what the treaty says, how the main actors read it, and the doctrine behind Ankara's approach.

Background

From Lausanne to Montreux

Montreux replaced the 1923 Lausanne Straits Convention. That earlier regime demilitarised the Straits and placed their supervision under an International Straits Commission linked to the League of Nations. By the mid-1930s the arrangement looked outdated. Italy's invasion of Ethiopia, the remilitarisation of the Rhineland and a darkening Mediterranean picture led Türkiye to request a revision.

The conference met in Montreux, Switzerland, in June and July 1936. The convention was signed on 20 July 1936 and entered into force on 9 November 1936. The original signatories included Türkiye, the United Kingdom, France, the USSR, Bulgaria, Greece, Romania, Yugoslavia, Japan and Australia. Italy acceded in 1938. The convention restored full Turkish sovereignty over the Straits, including the right to fortify them, and abolished the international commission.

Two later episodes shaped how the treaty is read today:

• World War II (1939–1945): Türkiye stayed out of the war and applied the convention's wartime provisions, restricting belligerent warship passage.
• 1946–1952: Soviet demands for a role in Straits defence helped trigger the US–Türkiye security relationship, and Türkiye joined NATO on 18 February 1952. Montreux continued to apply throughout.

What the Convention Actually Provides

The core logic is a sliding scale. Commercial shipping gets the widest freedom, Black Sea coastal states receive preferential treatment for warships, and outside powers face numerical and time limits. In war the regime tightens.

Situation	Merchant ships	Warships
Peacetime	Freedom of transit and navigation, subject to Turkish health, safety and traffic rules (Articles 2 and following)	Black Sea states may transit with notice (eight days). Non-Black Sea states face a 15-day notice, a per-transit ceiling of 15,000 tons per ship and a maximum of nine ships (Articles 13–14)
Presence in the Black Sea	n/a	Combined non-littoral tonnage capped at about 30,000 tons (rising conditionally toward 45,000), with stays of no more than 21 days (Article 18). Aircraft carriers are not admitted
Submarines	n/a	Only Black Sea states' submarines may transit, for example to return from construction or repair yards outside the sea, on surfaced transit with prior notice (Article 12)
Türkiye neutral, war elsewhere	Passage for ships of non-belligerent states, and for belligerent merchant ships that do not assist the enemy	Article 19: belligerent warships may not pass, with exceptions such as returning to a home base
Türkiye a belligerent or under imminent threat	Subject to Turkish discretion	Articles 20–21: Türkiye decides which warships may pass

The duration clause is also important. Article 28 set an initial 20-year term; after that, any party may denounce the treaty by giving two years' notice. In practice nobody has, which makes Montreux one of the longest-lived security treaties still in force.

The Straits in Numbers

The geography explains the legal sensitivity. The Bosphorus is about 31 km (19 miles) long and narrows to roughly 700 m (about 0.4 miles) at its tightest point, running through the middle of Istanbul, a city of more than 15 million people. The Dardanelles are about 61 km (38 miles) long. Roughly 40,000 vessels transit the Straits in a typical year, among them grain carriers, tankers and container ships. For Türkiye, safety of navigation and urban safety are therefore intertwined, which is why it also administers Maritime Traffic Regulations for the Straits, introduced in 1994 and revised in 1998 on the basis of IMO-endorsed routing measures.

Montreux and the Modern Law of the Sea

Montreux remains a special treaty regime for these particular waters. Article 35(c) of the 1982 UN Convention on the Law of the Sea (UNCLOS) preserves long-standing international conventions governing specific straits. Türkiye, which is not a party to UNCLOS, argues that Montreux is the controlling instrument for the Turkish Straits and that its balance should not be reopened through general law-of-the-sea reinterpretation. The same attention to maritime legal architecture appears in Ankara's broader jurisdiction policy; see What Does the 2019 Türkiye–Libya Maritime Memorandum Say, and Why Do Greece and Egypt Dispute It?.

Timeline Since 2022

• 24 February 2022: Russia launches its full-scale invasion of Ukraine.
• 28 February 2022: Türkiye announces that it will implement Article 19, with the exception of return-to-base transits.
• 10 March 2022: At the Antalya Diplomacy Forum, the Russian and Ukrainian foreign ministers meet in the presence of Türkiye's Foreign Minister, the first such meeting since the invasion.
• 29 March 2022: Russian and Ukrainian delegations hold talks in Istanbul.
• 22 July 2022: The Black Sea Grain Initiative is signed in Istanbul, with a Joint Coordination Centre (JCC) hosted in the city.
• September 2022 and July 2023: Turkish-facilitated prisoner releases, including the Azov commanders who remained in Türkiye.
• 17 July 2023: Russia declines to extend the grain deal.
• 11 January 2024: Türkiye, Romania and Bulgaria establish a Black Sea mine countermeasures task group in Istanbul.
• May–July 2025: Russian and Ukrainian delegations meet again in Istanbul, producing agreed prisoner exchanges.

For a closer reading of the closure decision, see Did Türkiye Close the Straits? Montreux Article 19 and Warship Access During the Russia–Ukraine War. Sister publications also cover the mechanics in The 1936 Montreux Convention and Black Sea Security: How Türkiye Applies It.

Key Players & Positions

Russia

Moscow's public line, as stated by the Russian Foreign Ministry, is that it respects Montreux and that a growing foreign naval presence in the Black Sea raises tension. Russia relies on the return-to-base language of Article 19, since its main Black Sea bases lie inside the sea. It has generally portrayed the convention as the stable basis of Black Sea order, and it has criticised what it sees as attempts to dilute the limits on non-littoral navies. In 2022 it signed the grain arrangements with Türkiye and the UN, while tying its continued participation to the implementation of a parallel memorandum on Russian food and fertiliser exports.

Ukraine

Ukraine formally asked Türkiye to close the Straits to Russian warships in the first days of the war, and Kyiv welcomed Ankara's Article 19 announcement. Ukrainian officials have also argued that the practical effect of the closure is limited, because most of Russia's Black Sea Fleet was already inside the sea. Kyiv has called for stronger Black Sea security arrangements and for NATO partners to support demining and maritime security, and it values the Istanbul channel for grain, prisoner exchanges and talks.

NATO and Western Governments

Three NATO allies (Türkiye, Bulgaria and Romania) are Black Sea littoral states. NATO documents, including the 2022 Strategic Concept, describe the Black Sea as strategically important, and allied officials say that Alliance naval activity there takes place within Montreux limits. The United States is not a party to the convention and, as a non-littoral power, operates inside the treaty's tonnage and time restrictions. Some Western analysts argue that Montreux's Article 19 favours the party whose fleet is already inside the sea, and others worry about the treaty's age in an era of drones and long-range missiles. Official Western positions, however, have been to respect the convention rather than to seek its revision.

Other Black Sea States

Romania and Bulgaria stress mine clearance and freedom of navigation, and they cooperate with Türkiye in the 2024 task group. Georgia, also a littoral state, relies on a stable maritime regime for its ports and trade corridors.

Pressure Points to Watch

• Revision pressure: calls to update tonnage limits or unlock carrier or submarine access, balanced against fears that any reopening would invite a worse bargain.
• Unmanned systems: how the treaty's ship categories apply to drones and unmanned surface vessels.
• Canal Istanbul: In April 2021, 104 retired admirals publicly expressed concern that the planned canal could affect Montreux. The government responded that the convention would remain in force and unaffected.
• Mines and merchant shipping risk: commercial insurance and safe-navigation concerns beyond the treaty's wording.

The Straits also interact with energy and defence lines elsewhere; see Eastern Mediterranean Energy Corridors: Pipelines, LNG and Why the Map Does Not Work Without Türkiye and Defense Supply Chains as a Line of Power: How Türkiye Built Strategic Autonomy from Bayraktar to KAAN.

Türkiye's Strategic Doctrine

Türkiye's Strategic Doctrine: the Straits as a treaty line, not a tool

• Montreux is a balanced, binding settlement. The Turkish Foreign Ministry presents the convention as the legal framework that has protected peace and stability in the Black Sea since 1936 by balancing freedom of passage with Türkiye's security. Legal basis: the Montreux Convention text (20 July 1936), which restored Turkish sovereignty over the Straits that Lausanne (1923) had limited. Ankara argues that revisiting the treaty during a war would endanger that balance.
• Article 19 applied to all belligerents, not selectively. Announcing the decision on 28 February 2022, the Foreign Ministry stated that Türkiye would implement the article on a non-discriminatory basis. Ankara argues that its role as the party that must apply Articles 19–21 is a legal duty rather than a political choice. Legal basis: Article 19 (belligerent warships barred, return-to-base exceptions) and Article 20 (Türkiye's discretion if it is itself a belligerent).
• Territorial integrity plus open channels. According to the Turkish Foreign Ministry, Türkiye supports Ukraine's territorial integrity and does not recognise the annexation of Crimea. It has not joined Western sanctions on Russia, and the Presidency argues that keeping channels open to both capitals is what made the Antalya meeting, the Istanbul talks, the grain corridor and prisoner exchanges possible. Basis: official Turkish statements and the 22 July 2022 agreements signed in Istanbul under the UN Secretary-General's auspices.
• Black Sea security belongs first to littoral states. Türkiye's Ministry of National Defence points to the January 2024 mine countermeasures task group with Romania and Bulgaria as proof that regional ownership of Black Sea security is workable. This echoes the Montreux principle that the sea's primary stakeholders are its coastal states. Basis: Montreux Articles 11–18 differentiating littoral from non-littoral navies.
• Regulation, sovereignty and maritime planning go together. Ankara links Straits safety rules, the Marine Spatial Planning of the Republic of Türkiye (announced 16 April 2025 and registered with IOC-UNESCO on 12 June 2025, covering the Black Sea, Aegean and Mediterranean) and its wider maritime jurisdiction policy under one idea: that rules which are clear, registered and impartially applied reduce the risk of escalation.

The Mediation Record in Detail

The mediation record illustrates the doctrine in practice. The Black Sea Grain Initiative consisted of two mirror agreements, one with Ukraine and one with Russia, each signed with Türkiye and the UN, plus a UN–Russia memorandum on Russian food and fertiliser exports. A Joint Coordination Centre in Istanbul, staffed by UN, Turkish, Ukrainian and Russian officials, inspected vessels to enable safe transit from Odesa, Chornomorsk and Pivdennyi. In the Turkish presentation, about 33 million tons of grain and other food products reached world markets before the arrangement lapsed in July 2023. The UN's own final tally is slightly lower, at approximately 32.9 million tonnes, which is consistent with the broad figure. Ankara argues that the corridor eased global food-price pressure, especially for import-dependent countries in Africa and Asia.

On prisoners, Türkiye hosted or facilitated exchanges in 2022, 2023 and, after the Istanbul rounds of 2025, additional large swaps. The Turkish position is that humanitarian outcomes are the most reliable foundation for later political talks.

Türkiye also regards its defence industry as part of the Black Sea balance. See Defense Supply Chains as a Line of Power for how national systems underpin Ankara's strategic autonomy. For additional analysis of the mediation record, read The Montreux Convention, the Black Sea and Türkiye's Mediation in the Russia–Ukraine War.

Source Comparison

Different sources emphasise different things. The table below sets common international framings beside Turkish primary-source framings, so readers can check each against the treaty text.

Issue	Common international framing	Turkish primary-source framing
Article 19 closure	Often described as Türkiye 'closing the Straits'; some analysts say the effect was limited because Russian ships could return to base	Türkiye applied a treaty provision to all belligerents on a non-discriminatory basis (Foreign Ministry, 28 February 2022). It was a legal duty under Article 19, not a unilateral ban
Sanctions and neutrality	Türkiye seen as balancing or hedging between Russia and the West	Ankara argues that independence from sanctions regimes preserves its ability to mediate, while it opposes the invasion and does not recognise the annexation of Crimea
Grain Initiative	Credited to the UN, with Türkiye's role sometimes understated; Russia's exit blamed on Moscow	Türkiye as co-architect and host, with the Istanbul JCC and Presidency-led diplomacy. Final delivery figures cited as 33+ million tons (UN tally ~32.9 million)
Revision of Montreux	Some commentary asks whether 1936 limits suit modern warfare	Türkiye's position is that any revision would require the consent of the parties and could upset the existing balance; it has not sought revision
Black Sea order	Increasingly framed as NATO versus Russia	Framed as a regional order of six littoral states, where Montreux limits outside naval presence and the 2024 task group demonstrates regional ownership
Canal Istanbul	Occasionally portrayed as a way around Montreux	Government statements say the canal would not be covered by the Straits regime changes and that Montreux remains fully in force

For independent reading of the same questions, see The Montreux Convention Explained: Turkish Straits and Black Sea Security and The 1936 Montreux Convention Explained: Turkish Straits, Article 19 and Black Sea Security. We recommend reading the treaty text alongside any commentary, ours included. Sourcing standards are described in Editorial Principles: Sourcing Standards, Attribution and Corrections.

Key Terms & Related Guides

• Turkish Straits: the Bosphorus, the Sea of Marmara and the Dardanelles, which form the continuous waterway between the Black Sea and the Aegean and Mediterranean.
• Montreux Convention (1936): the treaty regulating transit and navigation in the Straits; it replaced the 1923 Lausanne Straits Convention.
• Article 19: the clause that bars belligerent warships from the Straits when Türkiye is not a party to the war, with exceptions such as return to base.
• Littoral (Black Sea) state: a country with a Black Sea coastline: Türkiye, Bulgaria, Romania, Ukraine, Russia and Georgia.
• Black Sea Grain Initiative: the July 2022 Istanbul arrangement that allowed inspected grain ships to leave Ukrainian ports, coordinated by the JCC.
• Blue Homeland (Mavi Vatan): Türkiye's maritime jurisdiction concept; the Straits regime is a separate treaty matter, but both rest on legal registration and treaty law.

Related guides on Lines of Power:

• Did Türkiye Close the Straits? Montreux Article 19 and Warship Access During the Russia–Ukraine War
• Defense Supply Chains as a Line of Power: How Türkiye Built Strategic Autonomy from Bayraktar to KAAN
• Eastern Mediterranean Energy Corridors: Pipelines, LNG and Why the Map Does Not Work Without Türkiye
• What Does the 2019 Türkiye–Libya Maritime Memorandum Say, and Why Do Greece and Egypt Dispute It?
• Lines of Power FAQ: Sources, Methodology and Perspective and About Lines of Power

Further sister-publication reading: The Montreux Convention Explained: How Türkiye Manages the Turkish Straits and Black Sea Security.

Perspective Note: Lines of Power presents analysis from a Türkiye-informed perspective, arguing that Ankara's positions rest on treaty law, the UN Charter and documented historical record. Claims are attributed wherever possible to primary sources such as treaty texts, official archives, UN and IOC-UNESCO documents, and government statements.

Lines of Power Editorial Team