In the mid 1800s, the Emirate of Bohtan of Bedir Khan Beg span over parts of present day north eastern Syria. The demographics of this area underwent a huge shift in the early part of the 20th century. Ottoman authorities with the cooperation of Kurdish troops (and to a lesser degree, Circassian and Chechen tribes) persecuted Armenian and Assyrian Christians in Upper Mesopotamia and were granted their victims' land as a reward. Kurds were responsible for most of the atrocities against Assyrians, and Kurdish expansion happened at the expense of Assyrians (due to factors like proximity). Kurdish as well as Circassian 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.