What were causes of migration to Yasrib?

The idea of migration was born in the heart of the Holy Prophet(SAW) after the pledges of Aqabah. The people of Makkah hated and despised the Holy Prophet(SAW). The Holy Prophet(SAW) had struggled against his enemies for 30 years but it seemed that these people would not accept the right path until extreme struggle was made. He was well aware of the fact that the people involved in prejudice, superstition and ignorance would not abandon their beliefs and ways easily and that it would take extremist struggle to bring them on the right path.The people of Makkah struggled a lot to cease the expansion of Islam because this meant a threat to their beliefs and cultures they had been following from many years. So this necessitated the migration to Yasrib where people were willing to accept the Holy Prophet(SAW) in their city.