During the Ottoman Empire (1516–1922), large Kurdish-speaking tribal groups both settled in and were deported to areas of northern Syria from Anatolia. By the 18th century, five Kurdish tribes existed in northeastern Syria. The demographics of this area underwent a huge shift in the early part of the 20th century. Some Circassian, Kurdish and Chechen tribes cooperated with the Ottoman (Turkish) authorities in the massacres of Armenian and Assyrian Christians in Upper Mesopotamia, between 1914 and 1920, with further attacks on unarmed fleeing civilians conducted by local Arab militias. Many Assyrians fled to Syria during the genocide and settled mainly in the Jazira area. Starting in 1926, the region saw another immigration of Kurds following the failure of the Sheikh Said rebellion against the Turkish authorities. While many of the Kurds in Syria have been there for centuries, waves of Kurds fled their homes in Turkey and settled in Syrian Al-Jazira Province, where they were granted citizenship by the French Mandate authorities. The number of Turkish Kurds settled in al-Jazira province during the 1920s was estimated at 20,000 people, out of 100,000 inhabitants, with the remainder of the population being Christians (Syriac, Armenian, Assyrian) and Arabs.