At the commencement of the Muslim conquest of Egypt, Egypt is part of the Byzantine Empire with its capital at Constantinople.
However, it had been conquered just a decade before by the Persian Empire under Khosrau II (616 to 629 CE).
Emperor Heraclius recaptures Egypt after a series of campaigns against the Sassanid Persians, only to lose it to the Muslim Rashidun army ten years later.
Before the Muslim invasion of Egypt had begun, the Byzantines had already lost the Levant and its Arab ally, the Ghassanid Kingdom, to the Muslims.
All this leaves the Byzantine Empire dangerously exposed and vulnerable to the invaders.
