The Sasanian civil war of 589–591 was a conflict that broke out in 589, due to the great deal of dissatisfaction among the nobles towards the rule of Hormizd IV.

The civil war lasted until 591, ending with the overthrow of the Mihranid usurper Bahram Chobin and the restoration of the Sasanian family as the rulers of Iran.

The reason for the civil war was due to king Hormizd IV's hard treatment towards the nobility and clergy, whom he distrusted.

Khosrow was quite successful in these reforms, and after his death in 579, he was succeeded by his son Hormizd IV, who continued his father's policies, but in a harsher way; in order to control the elites, he, in the words of Shapur Shahbazi, "resorted to harshness, denigration, and execution.

Furthermore, Hormizd greatly reduced the pay of the military by 10 percent[2] and massacred many powerful and prominent members of the elite, including the famous Karenid vizier of his father, Bozorgmehr,[3] the latter's brother Simah-i Burzin; the Mihranid Izadgushasp; the spahbed ("army chief") Bahram-i Mah Adhar, and the Ispahbudhan Shapur, who was the father of Vistahm and Vinduyih.

[5][2] Bahram, infuriated by Hormizd's actions, responded by rebelling, and due to his noble status and great military knowledge, was joined by his soldiers and many others.

[7] The route taken by Bahram was presumably the northern edge of the Iranian plateau, where he repelled a Roman-funded attack by Iberians and others on Adurbadagan, and suffered a minor setback by a Roman force employed in Transcaucasia.

[8] Hormizd then left for the Great Zab in order to cut transmissions between Ctesiphon and the Iranian soldiers on the Roman border.

[8] Around that time the soldiers were situated outside Nisibis, the chief Iranian city in northern Mesopotamia; they however also rebelled against Hormizd and pledged their allegiance to Bahram.

[8] The loyalist forces eventually also rebelled and killed their commander, which made the position of Hormizd unsustainable, making him decide to navigate the Tigris river and take sanctuary in al-Hira, the capital of the Lakhmids.

[11] Khosrow then took a carrot and stick attitude, and wrote the following to Bahram; "Khosrow, kings of kings, ruler over the ruling, lord of the peoples, prince of peace, salvation of men, among gods the good and eternally living man, among men the most esteemed god, the highly illustrious, the victor, the one who rises with the sun and who lends the night his eyesight, the one famed through his ancestors, the king who hates, the benefactor who engaged the Sasanians and saved the Iranians their kingship—to Bahram, the general of the Iranians, our friend.... We have also taken over the royal throne in a lawful manner and have upset no Iranian customs.... We have so firmly decide not to take off the diadem that we even expected to rule over other worlds, if this were possible....

[8] This marked the beginning of a peaceful period between the two empires, which lasted until 602, when Khosrow decided to declare war against the Byzantines after the murder of Maurice by the usurper Phocas.