Final answer:
The main development of the Hijrah was caused by religious migration from Mecca to Medina.
Step-by-step explanation:
The main development of the Hijrah was caused by C. Religious migration from Mecca to Medina. In 622 C.E., Muhammad and his followers were forced to leave Mecca due to the persecution they faced. They found refuge in the nearby city of Medina, which became the base for the expansion of Islam and the starting point of the Islamic calendar.