Khosrow II in the context of "Muslim conquest of Persia"

Heraclius (Greek: Ἡράκλειος, romanized: Hērákleios; c. 575 – 11 February 641) was Byzantine emperor from 610 to 641. His rise to power began in 608, when he and his father, Heraclius the Elder, the Exarch of Africa, led a revolt against the unpopular emperor Phocas.

Heraclius's reign was marked by several military campaigns. The year Heraclius came to power, the empire was threatened on multiple frontiers. Heraclius immediately took charge of the Byzantine–Sasanian War of 602–628. The first battles of the campaign ended in defeat for the Byzantines; the Persian army fought their way to the Bosphorus but Constantinople was protected by impenetrable walls and a strong navy, and Heraclius was able to avoid total defeat. Soon after, he initiated reforms to rebuild and strengthen the military. Heraclius drove the Persians out of Asia Minor and pushed deep into their territory, defeating them decisively in 627 at the Battle of Nineveh. The Persian Shah Khosrow II was overthrown and executed by his son Kavad II, who soon sued for a peace treaty, agreeing to withdraw from all occupied territory. This way peaceful relations were restored to the two deeply strained empires.

The Byzantine–Sasanian War of 602–628, also called the Last Great War of Antiquity, was fought between the Byzantine Empire and the Sasanian Empire. It was the final and most devastating conflict of the Roman–Persian wars (54 BC – AD 628). The previous war between the two powers had ended in 591 after the emperor Maurice helped the Sasanian king Khosrow II regain his throne. In 602, Maurice was murdered by his political rival Phocas. Khosrow declared war, ostensibly to avenge the death of the deposed emperor Maurice. This became a decades-long conflict, the longest war in the series, and was fought throughout the Middle East, the Aegean Sea, and before the walls of Constantinople itself.

From 602 to 622, the Sassanians gradually conquered much of the Levant, parts of Anatolia, and—for the first time—Egypt and several islands in the Aegean Sea. The counter-attacks of the new Byzantine emperor Heraclius from 622 to 626 eventually forced the Persians onto the defensive. Allied with the Avars and Slavs, the Persians attempted to take Constantinople in 626, but were defeated. In 627, allied with Turks, Heraclius invaded the heartland of Persia. After the Battle of Nineveh (627), Iranian forces were finally broken, forcing civil war-torn Persia to seek peace.

The Sasanian civil war of 628–632, also known as the Sasanian Interregnum was a conflict that broke out after the execution of the Sasanian king Khosrow II between the nobles of different factions, notably the Parthian (Pahlav) faction, the Persian (Parsig) 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 four years and fourteen 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.

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.