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As the Ottoman Empire gradually shrank in size, some 7–9 million Turkish-Muslims from its former territories in the Caucasus, Crimea, Balkans, and the Mediterranean islands migrated to Anatolia and Eastern Thrace. After the Empire lost the Balkan Wars (1912–13), it lost all its Balkan territories except East Thrace (European Turkey). This resulted in around 400,000 Muslims fleeing with the retreating Ottoman armies (with many dying from cholera brought by the soldiers), and with some 400,000 non-Muslims fleeing territory still under Ottoman rule. Justin McCarthy estimates that during the period 1821 to 1922 several million Muslims died in the Balkans, with the expulsion of a similar number.

Millions of Muslims left the empire and migrated to what places?
Anatolia and Eastern Thrace