When Greece finally achieved its independence from the Ottomans, there were still some bugs to be worked out. It took four major wars before things settled down: the Greco-Turkish War of 1897, the First Balkan War from 1912 to 1913, WWI from 1914-1918, and the final Greco-Turkish War from 1919-1922. Once the dust settled, both countries thought it wise to clear each others’ ethnicities from their respective lands in 1923.
In reality, the mutual trade was more about religion than ethnicity. During Ottoman rule, many Orthodox Christians were living in Turkey, while a lesser number of Muslims lived in Greece. The trade essentially moved these people accordingly: Orthodox Christians to Greece and Muslims to Turkey. It mattered not that there were many native Greek Muslims who spoke only Greek, and a substantial number of native Turks who were Orthodox Christians and spoke only Turkish. The ‘exchange’, as it came to be known, was a watershed moment in the history of the modern Greek state, the end of centuries of rule by the Turks.
Those final years in their struggle for independence were especially hard for the Greek people. It is estimated that from 750,000 to 900,000 Greeks died at the hands of the Ottoman Turks. Even today, generations later, it remains a bitter chapter for both sides.