Why did Muslim people in the Middle East and other parts of Asia experience hardship during the time of the European Middle Ages?

A.
Their leaders, Muslim nobles, forced most Muslims to be serfs.

B.
Byzantine Christians forced their religion on Muslim people throughout the region.

C.
Western European crusaders conquered the Muslim empires and enslaved most of the people.

D.
They were repeatedly invaded and conquered by Mongol armies from central Asia.