Following the fall of the Byzantine Empire and the Turkish massacre of Greeks, there was the process of forced Islamization and mass exodus of the population from the Ottoman occupied lands. Sometime later when Islamic law was exercised, conversion to Islam was considered voluntary, but many did because of added status and economic benefit. The Janissary corps was a different matter as Greek boys were taken from their families, indoctrinated into Islam, and mandatorily assimilated into the Turkish armies.

Many of the Greeks from the islands and the mainland crossed the Adriatic and settled in Italy and Sicily. The Greeks of Pontus (the Black Sea coast) ended up to a large extent in Georgia. Of course there were repeated attempts after 1453 to chase the Turks out of mainland Greece and even many of the islands by both the Venetians and the Franks, and even to some extent by the Genoese, but the Greeks faired no better and often were left on their own to do battle when their sponsors gave up the fight. These rulers furthermore persecuted the Orthodox Church, contrary to the Turks who by Islamic law permitted tolerance of other religions. Furthermore the Catholic Christians were equally oppressive, and the Orthodox Christians suffered economically and even more so politically.

This was the case repeatedly in the Peloponnesus so that by 1699 when the Venetians acquired this area less than 90,000 inhabitants were found, the lowest number of people in recorded history. It was also reported that there were no more than 1.5 million Greeks left in the rest of the Balkans, Asiatic Turkey, and abroad.