World War I in Europe and the Russian Revolution (26 April 1915)
Historical Map of Europe
The Ottoman Turks had entered the War on the side of Germany in October 1914, threatening the Suez Canal and the Persian oil wells. Even more critically, supply routes to Russia's major ports were now blocked (by the Germans in the north and the Turks in the south). In an attempt to force open the southern route, the Allies landed at Gallipoli but were unable to break Turkish defenses.