The Greek genocide was the systematic killing of the Christian Ottoman Greek population of Anatolia which was carried out during World War I and its aftermath (1914–1922) on the basis of their religion and ethnicity. It was perpetrated by the government of the Ottoman Empire led by the Three Pashas, and the Government of the Grand National Assembly led by Mustafa Kemal Atatürk, against the indigenous Greek population of the Empire. The genocide included massacres, forced deportations involving death marches through the Syrian Desert, expulsions, summary executions, and the destruction of Eastern Orthodox cultural, historical, and religious monuments. Several hundred thousand Greeks died during this period. By late 1922, most of the Greeks of Asia Minor had either fled or had been killed. Those remaining were transferred to Greece under the terms of the later 1923 population exchange between Greece and Turkey, which formalized the exodus and barred the return of the refugees.