Sasanian civil war of 628–632

The Sasanian civil of 628–632, also known as the Sasanian Interregnum was a conflict that broke out after the execution of the Sasanian king Khosrau II between the Sasanian nobles of different factions, notably the Pahlav (Parthian) faction, the Parsig (Persian) faction, the Nimruzi faction, and the faction of general Shahrbaraz. Rapid turnover of rulers and increasing provincial landholder power further diminished the empire. Over a period of fourteen years and thirteen successive kings, the Sasanian Empire weakened considerably, and the power of the central authority passed into the hands of its generals, contributing to its fall.

Background
In 628, Khosrau II was overthrown by the feudal families of Iran, which included The Ispahbudhan spahbed Farrukh Hormizd and his two sons Rostam Farrokhzad and Farrukhzad. Shahrbaraz of Mihran family, the Armenian faction represented by Varaztirots II Bagratuni, and finally Kanadbak of the Kanārangīyān family. On 25 February, Kavadh II, along with Aspad Gushnasp, captured Ctesiphon and imprisoned Khosrau II. Kavadh II then proclaimed himself as king of the Sasanian Empire, and ordered Piruz Khosrow to execute all his brother and half-brothers, which included Mardanshah, the favorite son of Khosrau II. Three days later, Kavadh ordered Mihr Hormozd to execute his father (some sources state that he was shot to death slowly with arrows ). With the support of the Persian nobles, Kavadh then made peace with the Byzantine emperor Heraclius, which made the Byzantines regain all their lost territories, their captured soldiers, a war indemnity, along with the True Cross and other relics that were lost in Jerusalem in 614. Kavadh also took all the properties of Farrukhzad and put him under arrest in Estakhr. During this period, Piruz Khosrow assumed the leadership of the Parsig faction, while the Ispahbudhan Farrukh Hormizd, assumed the leadership of the Pahlav faction. Kavadh II later died from a devastating plague only after a few month's reign in 6 September 628. He was succeeded by his eight year old son Ardashir III.

Early phase of the civil war
During the reign of Ardashir III, Mah-Adhur Gushnasp was appointed as his minister, and administered the empire greatly. One year later, Shahrbaraz with a force of 6,000 men, marched towards Ctesiphon and besieged the city. Shahrbaraz, however, was unable to capture the city, and then made an alliance with Piruz Khosrow, the leader of the Parsig faction, and the previous minister of the Empire during the reign of Ardashir's father, Kavadh II. He also made an alliance with Namdar Gushnasp, the spahbed of Nimruz. Shahrbaraz, with the aid of these two powerful figures, captured Ctesiphon, and executed Ardashir III, along with Mah-Adhur himself, including other Sasanian nobles like Ardabīl. Forty days later, Shahrbaraz was murdered by Farrukh Hormizd, who then made Borandukht, the daughter of Khosrau II, ascend the throne. She then appointed Farrukh as the minister of the empire.

Borandukht was deposed by Shapur-i Shahrvaraz, the son of Khosrau II's sister Mirhran, and the Sasanian usurper Shahrbaraz. He was shortly thereafter deposed by Piruz and his faction, who did not acknowledge his rule. Piruz crowned Azarmidokht, the sister of Borandukht, as monarch of Persia.

Late phase of the civil war
Azarmidokht, under the advice of the Sasanian nobles, recalled Farrukhzad from his arrest and invited him to serve the Sasanians in high office once again. Farrukhzad, however, declined the invitation and refused to serve under a woman. He then retired to a fire-temple in Estakhr. After having crowned Azarmidokht, Farrukh declared himself as "the leader of the people and the pillar of Iran" and became king of parts of Iran. He then began to mint coins at Estakhr in Pars and Nahavand in Media under name of "Hormizd V". In order to make a union with the Parsig faction, and to seize power over all of Iran, Farrukh Hormizd asked Azarmidokht to marry him. Not daring to refuse, Azarmidokht had him killed with the aid of the Mihranid Siyavakhsh, who was grandson of Bahram Chobin, the famous spahbed and briefly shahanshah. She was shortly thereafter killed by Farrukh Hormizd's son Rostam Farrokhzad, who then restored Borandukht to the throne. Borandukht later met with the Pahlav and Parsig factions, with both factions agreeing to work together. Subsequently, Piruz later strangled Borandukht himself, which ended the Parsig-Pahlav collaboration and resumed their hostilities. However, Rostam and Piruz were threatened by their own men, agreed to work together once again, and crowned Yazdegerd III, the grandson of Khosrau II, as the new king of the empire.

Aftermath and impact
The Sasanian civil war greatly weakened the Sasanian Empire, and spread factionalism among the Sasanian nobles, who would later refuse to aid the Sasanians against the Arabs during the Islamic invasion of Iran.