How did Abu Bakr come to power?

Answer 1

The Abbasids came to power under the auspices of a Shi`ite movement which, they claimed, had transferred its loyalty to Muhammad b. `Ali, the great-grandson of Muhammad's uncle `Abbas. Intensive Propaganda began around 718 in Iraq and Khurasan.

Answer 2

The Abbassids were authoritarians. They ruled by Fiat and exerted a strong level of control over their territories. In the early Abbassid period, they presided over a very scientifically-oriented and tolerant regime towards minorities. As the rulers began to embrace Sunni Orthodoxy over Mu'tazilite Heresy, they began to be less scientifically-oriented. The toleration towards minorities remained, more-or-less.