The event called the hijra, which was marks the beginning of islam

Hijra or hijira was the migration of the prophet Muhammed(PBUH) and his followers from his homeland Mecca where he was rejected, as it was said by Prophet Issa (PBUH) a prophet is not accepted in his homeland, to Yathrib, where his message was accepted and ultimately led to islamic faith. The prophet later, as King,conguered mecca and converted it to islam.

Mohammad's departure from Mecca (going to Medina) in the year 622.

The hijra (also spelled "hijrah" or "hegira" in some variations of spelling in English) means an "exodus" or migration or movement.  Mohammad was warned of a plot in Mecca to assassinate him, by Mecca merchants who opposed him.  In Medina, Mohammad consolidated his following as the start of the Islamic movement, and returned to Mecca in 629 to conquer that city and prove that Allah was superior to the supposed gods of Mecca.