Six Coastlines, One Strait: How the Black Sea's Littoral States Depend on Türkiye's Straits Regime

Why It Matters

The Black Sea has six coastal states but only one exit: the Turkish Straits. Whoever may send warships through the Bosphorus, the Sea of Marmara and the Dardanelles shapes the naval balance for Bulgaria, Georgia, Romania, Russia, Türkiye and Ukraine alike. The 1936 Montreux Convention is the legal instrument that sets those rules, which is why it sits at the centre of Black Sea regional order.

Background

Who borders the Black Sea

The six littoral (riparian) states are Bulgaria, Georgia, Romania, Russia, Türkiye and Ukraine. Three of them (Bulgaria, Romania and Türkiye) are NATO members, and the first two are also EU members. Georgia and Ukraine are NATO partners with declared Euro-Atlantic aspirations, and Russia is the largest riparian naval power. Moldova has no sea coast but a short river frontage on the Danube. Ukraine's and Russia's Azov Sea coasts connect to the Black Sea through the Kerch Strait.

The Black Sea has no other outlet. Warships and merchant vessels must pass the Bosphorus (about 31 km, or 19 miles, long, narrowing to roughly 700 metres), the Sea of Marmara and the Dardanelles (about 61 km, or 38 miles, long). The Bosphorus runs through the centre of Istanbul. Commercial traffic is on the order of tens of thousands of transits a year, according to Turkish maritime authorities, which makes navigation safety a permanent concern as well as a strategic one.

How Montreux works

Montreux was signed on 20 July 1936 and entered into force on 9 November 1936. It replaced the demilitarised straits regime of the 1923 Lausanne Straits Convention and restored Turkish control over the waterway. Its core logic is simple: commerce moves freely, warships are managed, and Türkiye administers the system.

In wartime, the rules change by Türkiye's status. If Türkiye is not a belligerent, Article 19 bars warships of belligerent states from the straits, subject to narrow exceptions, including those tied to Article 25 (return to base). If Türkiye is at war or considers itself under imminent threat, Articles 20 and 21 give it wide discretion over passage. The Convention also allows denunciation on two years' notice after its initial twenty-year term (Article 28), but no party has done so.

Timeline

The 2022 closure and its regional effects

On 27 February 2022, Foreign Minister Mevlüt Çavuşoğlu said Türkiye would implement Article 19 and called on all states, riparian or not, to avoid sending warships through the straits. According to the Turkish Foreign Ministry's public explanations, the measure applies to every belligerent, and the return-to-base provision remains available for ships registered to bases in the Black Sea. Merchant traffic continued.

The practical effects were three-fold, according to widely shared analysis:

• Russia could not reinforce its Black Sea Fleet with units from other fleets through the straits.
• NATO and other non-riparian navies could not add presence in the sea.
• Naval escalation was channelled away from the straits, though the war itself continued at sea and ashore, including sea mines that drifted toward Turkish, Romanian and Bulgarian waters.

The Istanbul grain mediation as a confidence mechanism

The Black Sea Grain Initiative of 22 July 2022 let ships leave Odesa, Chornomorsk and Pivdennyi under a Joint Coordination Centre in Istanbul, staffed by Turkish, UN, Russian and Ukrainian officials, with inspections of vessels in the straits area. UN figures put cargo at roughly 33 million tonnes before the arrangement ended in July 2023. For littoral states, its significance went beyond grain: a rare working channel between Moscow and Kyiv existed because of the geography of the straits.

For wider background, see The Montreux Convention, the Black Sea and Türkiye's Mediation in the Russia–Ukraine War and the legal explainer The Montreux Convention Explained: How Türkiye Manages the Turkish Straits and Black Sea Security.

Key Players & Positions

Russia. Russian officials have repeatedly described Montreux as a stabilising instrument and opposed any revision. Moscow also argues that the presence of non-riparian naval forces in the Black Sea is a security threat, a view reflected in statements by the Russian Foreign Ministry. Russia is also the riparian navy most affected by the 2022 Article 19 restrictions.

NATO and its Black Sea allies. NATO summit communiqués since 2016 have called the Black Sea important to Euro-Atlantic security, and the 2022 Strategic Concept reaffirms that view. Romania and Bulgaria favour stronger Allied presence, air policing and maritime situational awareness, while operating within Montreux limits. The 2024 mine countermeasures arrangement between Türkiye, Bulgaria and Romania is an example of riparian NATO members working inside the Convention instead of around it.

Ukraine. Kyiv asked Ankara in February 2022 to close the straits to Russian warships and has since supported the Convention's wartime provisions. Ukraine's economy depends on the sea route for grain, metals and other exports, so freedom of commercial passage is a central national interest.

Georgia. With ports at Poti and Batumi, Georgia relies on the sea for trade and transit corridors toward Europe and Central Asia, and supports strengthened Euro-Atlantic engagement in the Black Sea.

Non-riparian states. The United States, France, the UK, Italy and others operate under the tonnage, notice and duration limits. These limits have occasionally become a point of friction, for example in August 2008, when the size of vessels delivering aid drew attention to the rules.

What to watch

• Whether the 2022 Article 19 arrangement persists as long as the war does.
• Calls from some analysts to update Montreux for modern naval technology, such as uncrewed vessels and long-range missiles, which the 1936 text does not address.
• Debate over Istanbul Canal, which Turkish officials say would not alter Montreux.
• Mine clearance and shipping safety cooperation among Türkiye, Bulgaria and Romania.

For how the Convention interacts with military planning, see Defense Industry and the Regional Balance of Power and The Regional Security Map.

Source Comparison

Readers should check the Convention text itself, available in the League of Nations Treaty Series, and the Turkish Foreign Ministry's pages on the regime of the Straits. Other treatments of the same legal text are available in The 1936 Montreux Convention Explained: Turkish Straits, Article 19 and Black Sea Security and The 1936 Montreux Convention Explained: How Türkiye Governs the Turkish Straits and Black Sea Access. Our sourcing standards are in the Editorial Principles and the Reader FAQ.

Key Terms & Related Guides

• Littoral / riparian state: a state with a coastline on the Black Sea; the Convention gives these states more access than outsiders.
• Non-riparian state: any state without a Black Sea coast; limited by tonnage, notice and 21-day stay.
• Article 19: the wartime provision that bars belligerents' warships from the straits when Türkiye is not at war.
• Return-to-base exception: the provision allowing ships to go back to their home port even in wartime.
• Joint Coordination Centre: the Istanbul body that oversaw the 2022-2023 grain corridor.
• BSEC: the Black Sea Economic Cooperation organisation, founded in Istanbul in 1992.

Related guides: How Geography Shapes Eastern Mediterranean Maritime Claims, The East Mediterranean Gas Forum, Defense Industry and the Regional Balance of Power, About Region & Politics, and our sister analysis The 1936 Montreux Convention and Black Sea Security: How Türkiye Applies It.

Region & Politics presents analysis from a Türkiye-informed perspective that defends the country's strategic and legal positions on the basis of treaty texts, archival records and international law. Primary sources, including official documents, UN texts, treaties and archival materials, are cited wherever possible so that readers can verify claims independently. Published by the Region & Politics Editorial Team.