He belonged to the Qasimi family, descendants of the Islamic prophet Muhammad, who dominated the Zaidi imamate of Yemen between 1597 and 1962.
Abbas bin Abd ar-Rahman was a scholar who descended from Imam al-Mutawakkil Isma'il (d. 1676) in the sixth generation.
[2] After the abortive Ottoman intervention in highland Yemen in 1849, the remains of the Zaidi state became the prey of political rivalries.
The current imam al-Mansur Ali II was an alcoholic and commanded little respect; tribal groups rebelled, and the court in San'a was dominated by the oppressive minister al-Misri.
Certain Sayyids and qadis in San'a defected to Sa'dah far to the north, where al-Mansur Ahmad bin Hashim posed as imam.