Having realized Russia’s need to acquire a seaboard, Peter began, in A.D. 1695-6, with the relatively easy conquest of Azov from the Turks. It is significant that, after his return from the Western tour of A.D. 1697-8, he addressed himself to the far more formidable task of conquering the Baltic Provinces from the Swedes, and persevered in this arduous enterprise for twenty years (A.D. 1700-21) until he finally achieved his aim. He had come to the conclusion that a seaboard on the Baltic was worth acquiring at any price because it would open the door for direct intercourse between Russia and the West. […] On the other hand, the conquest of Azov was not worth following up, because the further passage from this port to the open sea was blocked by the Ottoman Government’s control of the Straits of Kertch and of the Bosphorus and of the Dardanelles. And even if the Russian ships had been able to run the gauntlet of these three successive “Symplegades”, they would have merely found themselves at large in the Eastern Mediterranean – a sea which, in Peter’s day, before the opening of the short-cut from the Atlantic to the Indian Ocean, was a sluggish backwater, remote from the principal ocean-highways of the World.
Towards the end of the fifteenth century, Moscow (Ivan III) overcame the Golden Horde, and the Crimean khans (1449-1783), minor successors of the Horde, came under Ottoman protection. Russia did not conquer the Crimean Khanate (“Little Tartary”) until the Russo-Turkish War of 1768-74.
A Study of History, Vol III, OUP, 1934 (footnote)