The Ottoman Empire entered World War I on the side of the Central Powers and was ultimately defeated. The Ottomans successfully defended the Dardanelles strait during the Gallipoli campaign (1915–1916) and achieved initial victories against British forces in the first two years of the Mesopotamian campaign, such as the Siege of Kut (1915–1916); but the Arab Revolt (1916–1918) turned the tide against the Ottomans in the Middle East. In the Caucasus campaign, however, the Russian forces had the upper hand from the beginning, especially after the Battle of Sarikamish (1914–1915). Russian forces advanced into northeastern Anatolia and controlled the major cities there until retreating from World War I with the Treaty of Brest-Litovsk following the Russian Revolution (1917). During the war, the empire's Armenians were deported to Syria as part of the Armenian genocide. As a result, an estimated 600,000 to more than 1 million, or up to 1.5 million Armenians were killed. The Turkish government has refused to acknowledge the events as genocide and states that Armenians were only relocated from the eastern war zone. Genocidal campaigns were also committed against the empire's other minority groups such as the Assyrians and Greeks. Following the Armistice of Mudros on 30 October 1918, the victorious Allied Powers sought to partition the Ottoman state through the 1920 Treaty of Sèvres.