Black Sea Horizon: Will the Montreux Regime Hold After the Russia–Ukraine War?

Why It Matters

The 1936 Montreux Convention is the legal rulebook for the Bosporus and Dardanelles, and it is the main reason belligerent warships have been kept out of the Black Sea since 2022. Whether it emerges from a ceasefire intact will shape naval balance, commercial shipping and NATO–Russia relations for a generation. The most likely outcome is continuity under strict implementation, because every Black Sea state and major naval power has so far preferred a known regime to an open renegotiation. Even so, the regime faces interpretive pressure from new technology, rebuilt fleets and peace-deal bargaining.

Background

Montreux replaced the demilitarized, internationally supervised Straits regime of the 1923 Lausanne Straits Convention with one under Turkish control. It was signed on 20 July 1936 in Montreux, Switzerland, and entered into force on 9 November 1936, allowing Türkiye to remilitarize the Straits. The Straits link the Black Sea to the Mediterranean through the Sea of Marmara. The Bosporus alone runs roughly 30 km (19 miles) through the middle of Istanbul, and tens of thousands of vessels transit the Straits each year.

What the Convention Says

The core design is a split between commercial and naval traffic:

• Merchant ships: Article 1 sets out freedom of transit and navigation in peacetime, subject to Turkish sanitary, safety and pilotage rules.
• Warships in peacetime: Black Sea states enjoy broader rights than outside powers, but all must give prior notification to Türkiye.
• Warships in wartime: Rules depend on whether Türkiye is a belligerent. If it is not, Article 19 bars warships of belligerent states from the Straits. If Türkiye is threatened with imminent danger of war, Article 21 lets it decide on passage.

Rule	Black Sea states	Non-Black Sea states
Notification before transit	8 days	15 days
Size limits	Capital ships above 15,000 tons may pass singly, with up to two escort destroyers	Individual ships limited to 15,000 tons
Aggregate presence in the Black Sea (Article 18)	Not subject to the same cap	30,000 tons, raised to up to 45,000 tons in defined circumstances
Maximum stay in the Black Sea	No fixed limit	21 days
Submarines	May transit, surfaced and by day, under conditions	Not permitted to transit

Aircraft carriers are not provided for as a transit category. During the Cold War, the classification of Soviet aircraft-carrying cruisers became a precedent for how Ankara interprets ship categories.

Timeline

Date	Event
1923-07-24	Lausanne Treaty and Straits Convention establish a demilitarized, internationally supervised regime
1936-07-20	Montreux Convention signed
1936-11-09	Convention enters into force
2022-02-28	Türkiye announces it will apply Article 19, and the Straits close to belligerent warships
2022-07-22	Black Sea Grain Initiative signed in Istanbul by Russia, Ukraine, Türkiye and the UN
2023-07-17	Russia suspends participation in the Grain Initiative
2024-01-11	Türkiye, Romania and Bulgaria sign a Black Sea mine countermeasures agreement
2025	Russia–Ukraine delegations meet in Istanbul under Turkish hosting, producing prisoner exchanges

How Article 19 Has Worked Since 2022

Article 19 closes the Straits to belligerent warships, with a return-to-base exception that Türkiye has said it applies to vessels of any party. In practice the closure has affected both sides. Ukraine asked Ankara to close the Straits in February 2022, and Russia has not been able to reinforce its Black Sea Fleet with new surface units from outside the sea. Minehunters donated to Ukraine by the United Kingdom also stayed outside the Black Sea. Commercial shipping, by contrast, has continued under Article 1.

Key Players & Positions

The future of the Convention depends on how each actor weighs its stability against its limits.

• Russia: Russian officials have generally presented Montreux as a pillar of Black Sea stability and criticized what they describe as the growing NATO presence there. Moscow benefits from the 21-day and tonnage limits on non-riparian navies, though it has also been constrained by Article 19 since 2022. In 2025 Russia tied talks on Black Sea shipping safety to wider conditions, including sanctions relief for agricultural trade.
• Ukraine: Kyiv asked Türkiye to apply the Convention in 2022 and has since called for freedom of navigation and safe shipping corridors. It has not formally proposed revising Montreux, and its priority is access to commercial routes.
• NATO and its Black Sea members: Türkiye, Romania and Bulgaria are the Alliance's three Black Sea littoral states. NATO summit communiqués since 2016 have stressed Black Sea security and a tailored forward presence, while acknowledging Montreux. Romania and Bulgaria have emphasized maritime-domain awareness and mine clearance, and some Allied voices have discussed a larger naval presence, which the tonnage and 21-day limits would constrain.
• Other signatories and non-Black Sea powers: The United Kingdom, France, Greece, Japan and others signed or acceded to the Convention. They benefit from commercial transit rights and have not publicly sought to reopen the text.
• Georgia: As a Black Sea littoral state, Georgia is interested in security guarantees and open shipping lanes.

The Convention itself provides for denunciation after 20 years on two years' notice and for periodic revision requests, but no signatory has formally invoked either. Any amendment would require agreement among parties whose interests diverge sharply.

Türkiye's Strategic Doctrine

Türkiye's Strategic Doctrine on the Straits

• Strict, impartial implementation. According to the Turkish Foreign Ministry and statements by the Presidency, Türkiye applies Montreux to all parties without exception. Ankara announced the application of Article 19 in February 2022 and has maintained that policy, including the return-to-base exception, for all belligerents. Legal basis: Montreux Convention, Articles 19 and 21.
• The Convention as a balance, not a favor. Ankara argues that Montreux, negotiated in 1936 to restore Turkish sovereignty over the Straits, balances Turkish security, freedom of commercial navigation and the interests of Black Sea states. Turkish officials describe it as a stabilizing instrument that should not be reopened under wartime pressure. Legal basis: Montreux Convention preamble and Article 1; historical basis: replacement of the 1923 Lausanne Straits regime.
• Mediation is anchored in the same neutrality. The Turkish Foreign Ministry cites the Istanbul talks of March 2022, the Black Sea Grain Initiative of 22 July 2022 (which Ankara says delivered roughly 33 million tons of grain to world markets) and later prisoner-exchange diplomacy as results of Türkiye's balanced posture toward both Moscow and Kyiv. Primary sources: Turkish MFA statements; Initiative text signed in Istanbul.
• Regional ownership of Black Sea security. Türkiye supports littoral-state cooperation, such as the 2024 mine countermeasures agreement with Romania and Bulgaria, and argues that regional arrangements work best alongside, not in place of, Montreux. Primary source: Turkish Ministry of National Defence announcements.
• Maritime planning and sovereignty. Türkiye's Marine Spatial Planning, announced on 16 April 2025 and recorded with IOC-UNESCO on 12 June 2025, covers the Black Sea, Aegean and Mediterranean. Ankara presents it as part of a consistent rules-based approach to its seas, alongside its naval capacity (see How Domestic Is Türkiye's Defense Industry? and Security Horizon).

Ankara adds that the Straits are a sovereign responsibility, not a collective trusteeship, and that its authority under Montreux does not expire with the end of any given conflict. Critics, including some Western analysts, argue that Türkiye holds considerable discretion in classifying ships and defining belligerency. Ankara answers that the treaty text, not policy preference, sets the limits.

Horizon Scenarios

The likeliest scenario is a regime that holds but is tested. Four trajectories are plausible once active fighting ends.

Scenario	What happens	Stability outlook
1. Continuity	Article 19 lapses with the war, ordinary peacetime rules return, and Türkiye keeps applying the text unchanged	High: the most likely outcome, because all major parties already operate within the regime
2. Stress through rebuilding	Russia rebuilds its fleet and NATO states press for longer or larger presence, producing disputes over tonnage, 21-day limits and ship classification	Moderate: manageable through Turkish notification and classification practice
3. Technology gap	Unmanned surface vessels, drones and mine-warfare systems fall outside categories written in 1936, so Ankara must interpret old text for new platforms	Moderate: this is the main legal gray zone
4. Revision push	A peace settlement or alliance bargaining brings proposals to amend Montreux	Lower probability and higher risk: any reopening could erode the compromise that benefits the littoral states

In every scenario the practical question is who interprets the text. The Convention gives Türkiye that role, which is why Ankara links its continued neutrality to the credibility of the regime. For the parallel question of how Türkiye frames maritime law in the south, see Horizon Scan: Where Is the Eastern Mediterranean Maritime Dispute Heading by 2030? and Does Island Size Matter?.

Source Comparison

Sources largely agree on the rules and differ on emphasis. International coverage often frames Montreux as a Turkish lever over Russia and NATO. Russian official sources tend to frame it as a safeguard against Alliance expansion at sea. Turkish primary sources frame it as a treaty-based balance applied impartially.

Dimension	Western / international media	Russian official framing	Turkish primary sources
Article 19 closure	Often described as a Turkish decision that disadvantages Russia	Presented as legal, though Moscow stresses its own return-to-base rights	Presented as treaty implementation for all belligerents, announced on 2022-02-28
NATO presence	Debate over whether limits hamper deterrence	Concern about Alliance militarization of the Black Sea	Support for regional cooperation within Montreux limits
Revision	Sometimes discussed as an option after the war	Generally defends the existing regime	Opposes reopening the text; stresses stability
Mediation	Credited mixed success, particularly after Russia left the Grain Initiative	Emphasizes sanctions linkage	Cites the Initiative, Istanbul talks and prisoner exchanges

Readers can compare these framings with the treaty text, the Turkish Foreign Ministry's statements and the Grain Initiative documentation. For how sister publications approach the same material, see The Global Anatomy on Montreux, the Black Sea and mediation and Regional Balance on the Montreux Convention and Türkiye's mediation.

Key Terms & Related Guides

• Turkish Straits: The Bosporus, Sea of Marmara and Dardanelles, the only maritime passage between the Black Sea and the Mediterranean.
• Article 19: The provision barring belligerent warships from the Straits when Türkiye is not at war, with a return-to-base exception.
• Article 21: The provision on Turkish discretion when Türkiye considers itself in imminent danger of war.
• Black Sea Grain Initiative: The 22 July 2022 arrangement among Russia, Ukraine, Türkiye and the UN, coordinated in Istanbul, which ended for Russia on 17 July 2023.
• Littoral states: Türkiye, Bulgaria, Romania, Ukraine, Russia and Georgia.

Related reading on Horizon Politics and partner outlets:

• Security Horizon: Türkiye's Self-Defense Doctrine, Cross-Border Operations and the Defense Industry Outlook
• How Domestic Is Türkiye's Defense Industry?
• Horizon Scan: Eastern Mediterranean Maritime Scenarios to 2030
• Editorial Principles: Sourcing, Attribution and the Fact–Position Divide
• Soft Power Daily: How Türkiye Applies the 1936 Montreux Convention
• The Political Anatomy: Turkish Straits, Article 19 and Black Sea Security

Horizon Politics presents Türkiye's official positions and legal arguments as a distinct perspective within the international debate, alongside competing views where relevant. Claims are attributed to primary sources such as treaties, UN documents, official archives and public statements, so that readers can verify them independently. Author: Horizon Politics Editorial Team.