Military of the Sasanian Empire in the context of "Khosrow I"

As part of the early Muslim conquests, which began under Muhammad in 622, the Rashidun Caliphate conquered the Sasanian Empire between 632 and 654. This event led to the decline of Zoroastrianism, which had been the official religion of Persia (or Iran) since the time of the Achaemenid Empire, circa 550 BC. The persecution of Zoroastrians by the early Muslims during and after this conflict prompted many of them to flee eastward to India, where they were taken as refugees by various kings.

While Arabia was witnessing the rise of Islam in the 7th century, Persia was struggling with unprecedented political, economic and social issues as well as military weakness; the Sasanian army had greatly exhausted itself in the Byzantine–Sasanian War of 602–628. Following the execution of Sasanian shah Khosrow II in 628, Persia's internal political stability began to deteriorate rapidly, leading to ten new royal claimants being enthroned within the next four years. Shortly afterwards, Persia was further devastated by the Sasanian Interregnum, a large-scale civil war that began in 628 and resulted in the government's decentralization by 632.

The Sasanian conquest of Egypt took place between 618 and 621 CE, when the Sasanian Persian army defeated the Byzantine forces in Egypt and occupied the province. The fall of Alexandria, the capital of Roman Egypt, marked the first and most important stage in the Sasanian campaign to conquer this rich province, which eventually fell completely under Persian rule within a couple of years.

Siyawush (also spelled Siyavash), known in Byzantine sources as Seoses (Σεόσης), was an Iranian officer, who served as the head of the Sasanian army (arteshtaran-salar) during the second reign of the Sasanian king (shah) Kavad I (r. 498–531). In c. 520, he was accused of purposely misusing peace negotiations with the Byzantine Empire, and was thus removed from power and executed.

The Lakhmid kingdom (Arabic: اللخميون al-Lakhmiyyūn), also referred to as al-Manādhirah (المناذرة) or as Banū Lakhm (بنو لخم), was an Arab kingdom that was founded and ruled by the Lakhmid dynasty from c. 268 to 602. Spanning Eastern Arabia and Southern Mesopotamia, it existed as a dependency of the Sasanian Empire, though the Lakhmids held al-Hira as their own capital city and governed from there independently. The kingdom was a participant in the Roman–Persian Wars, in which it fought as a Persian ally against the Ghassanid kingdom, which was ruled by a rival Arab tribe and existed as a dependency of the Roman Empire. While the term "Lakhmids" has been applied to this kingdom's ruling dynasty, more recent scholarship prefers to refer to them as the Naṣrids.

The Nasrid dynasty's authority extended over to their Arab allies in Al-Bahrain (eastern cost of Arabia) and Al-Yamama. In 602, the Persian king Khosrow II deposed and executed the last Nasrid ruler Al-Nu'man III and annexed the Lakhmid kingdom, triggering a revolt by his Arab allies in Najd. The ensuing disorder between anti-Persian rebels and pro-Persian loyalists in the kingdom culminated in the Battle of Dhi Qar, which resulted in a defeat for the Persian army and their loyalists, thereby ending the Persian hegemony over Eastern Arabia. The success of the rebellion and the victory against the Persians at Dhi Qar roused political confidence, enthusiasm, and self-consciousness among the Arabs. Coupled with increasing instability in Persia proper after the downfall of Khosrow in 628, these events heralded the decisive Battle of Qadisiyya in 636 and the Muslim conquest of Persia.

Spāhbad (also spelled spahbod) is a Middle Persian title meaning "army chief" or commander used chiefly in the Sasanian Empire. Originally there was a single spāhbad, called the Ērān-spāhbed, who functioned as the generalissimo of the Sasanian army. From the time of Khosrow I (r. 531–579) on, the office was split in four, with a spāhbad for each of the cardinal directions. After the Muslim conquest of Persia, the spāhbed of the East managed to retain his authority over the inaccessible mountainous region of Tabaristan on the southern shore of the Caspian Sea, where the title, often in its Islamic form ispahbedh (Persian: اسپهبذ; in Arabic: اصبهبذ ʾiṣbahbaḏ), survived as a regnal title until the Mongol conquests of the 13th century. An equivalent title of Persian origin, ispahsālār or sipahsālār, gained great currency across the Muslim world in the 10th–15th centuries.

The title was also adopted by the Armenians (Armenian: սպարապետ, [a]sparapet) and the Georgians (Georgian: სპასპეტი, spaspeti), as well as Khotan (spāta) and the Sogdians (spʾdpt) in Central Asia. It is also attested in Greek sources as aspabedēs (ἀσπαβέδης). The title was revived in the 20th century by the Pahlavi dynasty, in the Modern Persian form sepahbod (سپهبد), equivalent to a three-star Lieutenant General, ranking below arteshbod (full General).