Why a 90-year-old treaty limits NATO in the Black Sea
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- Montreux Convention, signed July 20, 1936, restores Türkiye's sovereignty over the Dardanelles and Bosporus straits — a bottleneck just 700 meters wide at its narrowest point that gates all Black Sea access
- Türkiye invoked Article 19 after Russia's February 2022 invasion, barring belligerent nations' warships from the straits and keeping "up to 30 Russian ships" outside the Black Sea, which Carnegie Europe's Thomas de Waal says gave Ukraine "the upper hand"
- Ukraine never built warships and instead "shifted the generation of attack" to drones and modern technology not covered by the 1936 treaty, exploiting gaps the Montreux drafters couldn't anticipate
- The United Kingdom donated two minesweepers to Ukraine in 2024, but Türkiye classified them as "vessels of war," leaving both ships docked in Portsmouth, England, with no Black Sea access
- Romania is spending €2.5 billion ($2.8 billion) to expand Mihail Kogalniceanu Air Base near Constanța into what the source describes as the largest NATO military base in Europe — bigger than Ramstein in Germany
- NATO lacks a continuous Black Sea fleet presence because of Montreux; at the recent Ankara summit, Türkiye, Romania, and Bulgaria announced a trilateral mine-clearing task group as the alliance's workaround
- The treaty still references the League of Nations — defunct for 80 years — and de Waal says "no one wants to touch it," because renegotiation would mean reopening talks with Russia
Why it matters: Türkiye's wartime invocation of Article 19 blocked roughly 30 Russian naval reinforcements from reaching the Black Sea — a structural edge experts say helped Ukraine survive without a conventional fleet. With Romania now pouring €2.5 billion into a new mega-base near Constanța, NATO is spending billions to work around a treaty that hands Ankara effective veto power over any alliance escalation in the region.
