The Caliphate is not allowed to force any non-Muslim to abandon his/her belief. Rather the non-Muslims should accept Islam after being intellectually convinced of the Islamic belief.
Allah (Most High) says:
لا إِكراهَ فِي الدّينِ
“There is no compulsion in religion”
Before the Ottomans liberated Bosnia, it was one of the only Balkan regions without a strong allegiance to Christianity. An independent Bosnian Church had been established in the 11th century, outside the jurisdiction of either the Catholic or Orthodox Churches, but even that was on shaky ground by the time the Ottoman’s arrived in the 15th century.
Most scholars have rejected the old theory that Bosnia became a Muslim state because of an influx of Muslims that came to the region following the Ottoman invasion. Ottoman census figures show that there was in fact very little migration to Bosnia by the Turks; the increasing number of Muslims was due to the conversion of Bosnians already living in the region.
In 1468-9, just after the Ottoman conquest of Bosnia, the Ottomans recorded approximately 185,000 Christians living there, as opposed to 1,700 Muslims.
By 1485, the figure was 155,000 Christians and 22,000 Muslims.
By 1520, there were about 98,000 Christians and 84,000 Muslims, and by 1600 the Muslims were the majority in Bosnia.
Considering that the overall population did not significantly rise over this period, it is apparent that there was no influx of Muslims from outside the region; the Bosnians themselves simply converted.