During the caliphate of al-Mutawakkil, Saleh ibn Nasr occupied Sistan on the pretext of driving out the Kharijites. In order to repulse the forces of Tahir ibn Abdollah, the ruler of Khorasan, he sought help from Yaqoub ibn Layth Saffar, who had made somewhat of a name for himself. Saleh was succeded by his brother Dirham ibn Nasr, who appointed Yaqub as the general of his army.
In the year 861 CE Yaqub seized the rule of Sistan from Dirham and began to expand the territory under his control. First he turned to the east and after occupying Bost captured Kabol from Ratbil, its independent ruler. Then he captured Harat from the Tahirids, but instead of extending his conquests to the north set out in 868 CE for Kerman. He wrested Shiraz from the control of the caliph's governor but nevertheless continued to call himself a vassal of the caliph, the Abbasid al-Mutazz Billah.
In 869 CE he returned to Zaranj, his capital, and in 871 CE, during the caliphate of al-Mutamid Billah, the successor of al-Muhtadi, went once again to Shiraz. Thecaliph was able to prevent him from attacking Baghdad by appointing him governor of Balkh, Tokharestan, Fars, Kerman, Sistan and Sind. In 259/873, in order to bring Khorasan under his control, Yaqoub invaded Neishapour, where Mohammad ibn Tahir surrendered to him. From Khorasan Yaqoub went to Gorgan and Tabarestan (today Mazandaran) and then as far as Chalous in pursuit of Hassan ibn Zayd Alawi, who fled to Gilan. Then for a third time he invaded Fars, advancing as far as Khouzestan. Seventy kilometers from Baghdad, at Deyrol-aqul, he met the forces of the caliph but was defeated and returned to Khouzestan. In the year 878 CE he died from colic at Jondishapour.
Yaqoub's brother and successor, Amr ibn Layth, acknowledged the authority of the caliph and was thereby granted the governorship of Fars, Kerman, Esfahan, Kuh-ha (the mountains, i.e. the region of Jebal or today's Eraq-e-Ajam and Qohestan, Gorgan, Tabarestan, Sistan and Sind (i.e. the regions inhabited by Muslims and bordering on the Indus River). In order to force Amr into a confrontation with Amir Ismail Samani, who had newly come to power in Transoxania, the caliph also issued a firman for the rule of Transoxania in Amr's name. Unaware of the caliph's ploy Amr went to war with Ismail in order to assert his authority in Transoxania and in 900 CE was defeated and captured.
The territories of the Saffarids reached the limit of their expansion during the rule of Yaqoub and his brother Amr. To the cast they extended to the Indus River and to the northeast to the Oxus. In the north and northwest all of Khorasan, Gorgan and Tabarestan were Saffarid territory and in the south the Saffarids occupied Kerman and Fars. However, Khouzestan can not be considered as part of Saffarid territory.
After Amr the domain of the Saffarids was limited to Sistan and the Saffarid princes were the vassals of the powerful Iranian dynasties which came into existence one after another, such as the Samanids, the Ghaznavids, the Khwarazm-Shahs, the Il-Khanids, the Karts, the Timurids and the Safavids.