At the commencement of the Muslims conquest of Egypt, Egypt was part of the Byzantine Empire

Byzantine Empire

The Byzantine Empire was the Eastern Roman Empire during the periods of Late Antiquity and the Middle Ages, centred on the capital of Constantinople. Known simply as the Roman Empire or Romania to its inhabitants and neighbours, the Empire was the direct continuation of the Ancient Roman State...

 with its capital in Constantinople

Constantinople

Constantinople was the capital of the Roman, Eastern Roman, Byzantine, Latin, and Ottoman Empires. Throughout most of the Middle Ages, Constantinople was Europe's largest and wealthiest city.-Names:...

. However, it had been occupied

Siege of Alexandria (619)

Between 618 and 621 AD, the Sassanid Persian army defeated the East Roman 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 Sassanid campaign to conquer this rich province, which eventually fell...

 just a decade before by the Persian Empire

Sassanid Empire

The Sassanid Empire , known to its inhabitants as Ērānshahr and Ērān in Middle Persian and resulting in the New Persian terms Iranshahr and Iran , was the last pre-Islamic Persian Empire, ruled by the Sasanian Dynasty from 224 to 651...

 under Khosrau II (616 to 629 AD

Anno Domini

and Before Christ are designations used to label or number years used with the Julian and Gregorian calendars....

). Emperor Heraclius

Heraclius

Heraclius was Byzantine Emperor from 610 to 641.He was responsible for introducing Greek as the empire's official language. His rise to power began in 608, when he and his father, Heraclius the Elder, the exarch of Africa, successfully led a revolt against the unpopular usurper Phocas.Heraclius'...

 re-captured Egypt after a series of campaigns against the Sassanid Persians, only to once again lose it to the Rashidun army

Rashidun army

The Rashidun Caliphate Army or Rashidun army was the primary military body of the Rashidun Caliphate's armed forces during the Muslim conquests of the 7th century, serving alongside the Rashidun Navy...

 ten years later. Before the Muslim

Muslim

A Muslim, also spelled Moslem, is an adherent of Islam, a monotheistic, Abrahamic religion based on the Quran, which Muslims consider the verbatim word of God as revealed to prophet Muhammad. "Muslim" is the Arabic term for "submitter" .Muslims believe that God is one and incomparable...

 invasion of Egypt began, the Byzantine Empire had already lost the Levant

Levant

The Levant or ) is the geographic region and culture zone of the "eastern Mediterranean littoral between Anatolia and Egypt" . The Levant includes most of modern Lebanon, Syria, Jordan, Israel, the Palestinian territories, and sometimes parts of Turkey and Iraq, and corresponds roughly to the...

 and its Arab ally, the Ghassanid Kingdom

Ghassanids

The Ghassanids were a group of South Arabian Christian tribes that emigrated in the early 3rd century from Yemen to Syria, Jordan, Lebanon and the Holy Land....

, to the Muslims. This all left the Byzantine Empire dangerously exposed and vulnerable to the invaders.
At the dawn of the seventh century A.D, Egypt

Egypt

Egypt , officially the Arab Republic of Egypt, Arabic: , is a country mainly in North Africa, with the Sinai Peninsula forming a land bridge in Southwest Asia. Egypt is thus a transcontinental country, and a major power in Africa, the Mediterranean Basin, the Middle East and the Muslim world...

 was held in fee for the Byzantine Empire.