Recurrent controversy in the 19th–20th centuries over the passage of warships through the Bosporus and Dardanelles straits between the Black Sea and the Aegean and Mediterranean seas.
Both straits were in Turkish territory, but when Russia gained control of the northern shore of the Black Sea, its ships were given free passage. Russia sought to control the passage of non-Turkish ships with the Treaty of Lausanne (1923) allowed free passage to all warships, until it was revised by the {{link=Montreux Convention">Montreux Convention (1936) to reestablish Turkey's right to restrict access by navies of non-Black Sea states.