Ya'qub attracted the attention of an Abbasid caliph by first battling Kharijites in his homeland of Sistan. In 864, "Yaʿqub led an expedition to Bost against his former master Ṣāleḥ, and then into Roḵḵaj and Zamindāvar against the local ruler there, the Zunbil, killing him and securing an immense booty." His army then marched to Ghazna, Kabul, and Bamyan, conquering these territories in the name of Islam by appointing Muslim governors. From there they moved to north of the Hindu Kush and by 870 AD the whole of Khorasan was brought under their control.
In 873, Ya'qub ousted the Taharids from their own capital of Nishapur, which led to conflicts with the Abbasid caliphate. In 874, he traversed to Tabaristan and battled the Zaydi leader al-Hasan b. Zaydi. Ya'qub collected taxed in Tabaristan's capital Amul before departing for Rayy. In 875, Ya'qub again marched to Fars, though the reason behind this is unclear. In 876, the Abbasid representative Mutawaffiq, offered Ya'qub governorship of Khurasan, Tabaristan, Jurjan (Gorgan), Rayy, and also the position of security-head in Madinat al-Salam. Yaqub requested a personal visit with the caliph Mu'tamid before he accepted the governorships. Once the caliph had reached Baghdad, Yaqub did not pay him a personal visit as he had initially requested, but instead fought the caliph at the battle of Dar al-Akul and was defeated. Yaqub then withdrew from Iraq and died three years later. He is sometimes perceived as one of the first autonomous rulers in Khurasan since the Islamic conquests.
The motivation behind the Saffarids' initial campaigns remains unknown and highly debated in secondary scholarship. Some scholars believe that Yaqub fought as a ghazi warrior for the purpose of spreading proto-Sunni Islam, others support the notion that he was motivated by his Persian identity and consequent desire to restore the glorious Sasanian past, while still others believe he was simply motivated by greed and adrenaline. During one of his numerous battles, his face was disfigured to where he could only eat through a pipe in his mouth for twenty days.
It was during his rule that Persian was introduced as an official language, and Yaqub reportedly did not know Arabic. Laith has been accorded the historical status of a popular folk hero since his court began the revitalization of the Persian language after two centuries in which the Arabic language flourished in Persian lands.
Read more about this topic: Ya'qub-i Laith Saffari