The Ottoman conquest of Bulgarian territories caused demographic changes. They followed as a consequence of the demographic loss, suffered by the Bulgarians during the conquest and of the deportation of Bulgarian population to Asia Minor. In Thrace, Dobrudzha and Ludogorie regions settled Muslim colonists, who established new settlements and town centres. This created conditions for the spread of Islam among the Bulgarian Christian population.
Although the Christians in the Ottoman Empire had the status of zimmi, i.e. subjects of the Sultan and as such had the right to practice Christianity, this status did not protect them against purposeful attempts of the state at religious assimilation.
The adoption of Islam brought some tax concessions but did not change their status. It was quite different with young male Christians who were taken in the form of a tax (devshirme) to man the janissary corps. After the adoption of Islam, they became members of the group of the military, some had positions in the Sultan's court and some in the administration of the Empire.
The everyday way of life of Christians and Muslims in villages and towns predetermined the forms and methods of Islamization. In some cases this was voluntary adoption of Islam, be it because of marriage of a Christian woman to a Muslim, be it because of tax concessions, and often due to conviction born by the influential propaganda.
Islam however was very often imposed forcefully, accompanied by atrocities. The memory of them is kept alive in history till this very day.
Even today we can see the consequences of the Islamization of the Rhodope region and of some villages near Teteven. The Muslims living there speak Bulgarian and are called pomaks. This is a compact population and for that reason they are often given as an example of forceful Islamization.