Why was the hijra a turning point for islam?

The Hijrah or Hegira was around since the beginning of the Islamic religion. This is a journey to Mecca and Medina, the two holy cities of the Arabian Peninsula. People from all around the world (commonly Muslims) go to Mecca to circle seven times around the holy Kaaba. This was another turning point because of its history. The prophet Muhammad (Peace Be Upon Him) began to travel but there were men of the Quraysh who wanted to kill him the next morning. His cousin posed as Muhammad and lay in his bed the day after he left and the assassins were tricked. He and his father-in-law, Abu Bakr, continued there journey to Mecca. Midway, Suraqa bin Malik of the Kennah tribe pursued them. Each time his horse would near the prophet's group, it would stumble. They changed their direction to Medina and participated in the Friday prayer in its city. 

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Im migration prohibition.