As the Fatimid state was at the time too weak to attempt a direct invasion, they found another means of revenge. Between the Nile and the Red Sea were living Bedouin nomad tribes expelled from Arabia for their disruption and turbulency.  The Banu Hilal and the Banu Sulaym for example, who regularly disrupted farmers in the Nile Valley since the nomads would often loot their farms. The then Fatimid vizier decided to destroy what he couldn't control, and broke a deal with the chiefs of these Beduouin tribes. The Fatimids even gave them money to leave.