Following Timur's death in February 1405, Umar and his brothers fought incessantly amongst themselves and with their father Miran Shah, as well as with neighbouring princes.
Amirs migrated freely between them, and when the princes ran out of money for their troops, they were forced to reward them instead by allowing the plunder of their own provinces. About a month after Timur's death, Jahanshah bin Cheku, having become increasingly estranged from Umar, rose up against him. While Umar was conferring with advisors in his tent, Jahanshah came to the door and killed some of those closest to the prince. However, finding himself outnumbered, Jahanshah fled, and was pursued and killed. Historian
Beatrice Forbes Manz suggests that Jahanshah had been aspiring to rule Azerbaijan, either through Umar or in his own name. Around this time, Umar's brother
Abu Bakr, having lost his own province to
Sultan Ahmad Jalayir, joined Umar in Azerbaijan alongside Miran Shah. However, the princes soon began to disagree, and Umar imprisoned Abu Bakr in
Soltaniyeh and had his army plundered. However, Abu Bakr escaped, taking with him the city's treasury. Joining up in
Khorasan with Miran Shah (who had withdrawn out of fear that Umar might imprison him also), both father and son then returned and captured Soltaniyeh. Umar, deserted by many
amirs, retreated to
Maragheh. There, he gathered a new army of
Barlas,
Suldus, and
Turkmen soldiers. He headed to
Tabriz with the intention of fortifying himself, though was denied entry by the population, who had too recently suffered from the extortion of Umar's officials. On hearing of the approach of Abu Bakr, Umar went to
Fars to solicit the aid of his cousins,
Pir Muhammad,
Rustam, and
Iskandar, sons of the late
Umar Shaikh. Together, they fought Abu Bakr and Miran Shah in April 1406, though were defeated. The beaten princes were pursued to
Isfahan, held by Rustam, where they were unsuccessfully besieged by Abu Bakr. The sons of Umar Shaikh subsequently withdrew to their own strongholds, while Umar sought refuge with his uncle
Shah Rukh in Khorasan. Shah Rukh granted him the rule of
Mazandaran, though, according to the
Castilian ambassador
Ruy de Clavijo, Umar harboured designs on the throne itself. He revolted within six months and was defeated by Shah Rukh in an engagement near
Jam. ==Death==