After the death of his brother, Farrukhzad became the spahbed of Khorasan and Azarbaijan, he then gathered an army at Azarbaijan to prepare for the next battle against the Arabs.
Farrukhzad became the spahbed of Khorasan and Azarbaijan. This was what he gathered an army at Azarbaijan. This was after the death of his brother. This was to prepare for the next battle against the Arabs.