Kurdish population the figure at 10 to 15 million Kurds in Turkey. Kurds mostly live in Northern Kurdistan, in Southeastern and Eastern Anatolia. But large Kurdish populations can be found in western Turkey due to internal migration. According to Rüstem Erkan, Istanbul is the province with the largest Kurdish population in Turkey. From the 7 million Iranian Kurds, majority who are Sunni. Shia Kurds inhabit Kermanshah Province, except for those parts where people are Jaff, and Ilam Province Province; as well as some parts of Kurdistan, Hamadan and Zanjan provinces. The Kurds of Khorasan Province in northeastern Iran are also adherents of
Population exchange between Greece and Turkey a legitimizing factor or a "safe criterion" in marking ethnic groups as Turkish or as Greek in the population exchange. As a result, the Greek-Turkish population exchange did exchange the Greek-Orthodox population of Anatolia, Turkey and the Muslim population of Greece. However, due to the heterogeneous nature of these former Ottoman lands, many other ethnic groups posed social and legal challenges to the terms of the agreement for years after its signing. Among these were the Protestant and Catholic Greeks, the Arabs, Albanians, Russians, Serbians, Romanians of the Greek Orthodox religion; the Albanian, Bulgarian, Greek Muslims of Macedonia and Epirus,