The beginning of revelation to the Prophet Muhammad and the proselytizing of absolute monotheism marked the Mecca period. When the persecution of Muslims and the Prophet became intolerable, they decided to emigrate to Yathrib (later known as Medina), about two hundred miles north of Mecca. Islamic history calls this event Hijra. It occurred in 622 CE and is the basis of Islamic chronology. Muslims date their history not from the Prophet's birth nor from his reception of the first revelation in 610. Instead, they date it from the creation of the Islamic community (Ummah) in Medina. With this migration, the Meccan period of spiritual ignorance ended, and the Islamic age of enlightenment began. Islam took on a political form to establish an Islamic community-state at Medina to realize God's will on earth.
Mecca had a relatively homogenous population belonging to the Quraysh tribe with strong leadership. Medina had a heterogeneous population; there were two Arab tribes and three main Jewish tribes. The city was polarized on tribal lines, and many bloody battles had already occurred. The Prophet's first task was to bring unity and restore peace to the oasis. The task was not easy; however, in the end, he succeeded in awakening a spirit of union unknown to the city's history. During the Medina period, all major battles occurred with Pagans of Arabia and the Jews of Medina (please refer to Volume 5 for all battle descriptions)
For the remaining ten years of his life, his personal history merged with that of the Medinese commonwealth, of which he was the center. The Medinese found the Prophet to be a master whom it was difficult not to love and obey. He had, as one biographer wrote, "the gift of influencing men, and he had the nobility only to influence them for good."