During World War I , the Ottoman Empire entered the conflict on the side of Germany and the Austro-Hungarian Empire . It ultimately suffered defeat and loss of control of the entire Near East to the British Empire and French Empire . During the conflict , genocide against indigenous Christian peoples was carried out by the Ottomans and their allies in the form of the Armenian Genocide and Assyrian Genocide , of which Deir ez-Zor , in Ottoman Syria , was the final destination of these death marches . In the midst of World War I , two Allied diplomats ( Frenchman François Georges-Picot and Briton Mark Sykes ) secretly agreed on the post-war division of the Ottoman Empire into respective zones of influence in the Sykes-Picot Agreement of 1916 . Initially , the two territories were separated by a border that ran in an almost straight line from Jordan to Iran . However , the discovery of oil in the region of Mosul just before the end of the war led to yet another negotiation with France in 1918 to cede this region to ' Zone B ' , or the British zone of influence . This border was recognized internationally when Syria became a League of Nations mandate in 1920 and has not changed to date
Armenian Genocide
Armenian Genocide
Syria