Final answer:
The Byzantine Empire gained territories initially but later lost significant regions, mainly in the eastern Mediterranean and North Africa, to Islamic conquerors from the seventh century onwards. Despite numerous geopolitical and socio-religious challenges, the empire survived for centuries, preserving its Eastern borders against diverse rivals.
Step-by-step explanation:
After 330 CE, the Byzantine Empire experienced a series of territorial changes. Initially, following a period of expansion, the empire encompassed a vast region that included areas such as North Africa and Egypt. However, with the rise of Islamic conquests in the seventh century, the empire suffered significant territorial losses, particularly in the east. Vast stretches of the eastern Mediterranean coast and many territories across North Africa, once part of the empire, were taken by Islamic conquerors and were largely never recovered. These losses marked a significant reduction in the empire's extent compared to its boundaries at the time of Constantine I.
The empire weathered centuries of geopolitical instability, socio-religious change, and economic crises. Despite these challenges and territorial reductions, the Byzantine Empire managed to preserve its cultural and religious influence in the regions it continued to control and, at various times, even managed to regain some of its lost territories. Nevertheless, from the seventh to early thirteenth century, Byzantium was predominantly engaged in defending and attempting to preserve its eastern borders against diverse rivals, including emerging Islamic polities and European adversaries.