During whose caliphate did the significant conquest of large portions of the Byzantine territories, including Syria and Egypt, largely take place?

Explanation

– The significant conquest of large portions of Byzantine territories, including Syria and Egypt, largely took place during the caliphate of Umar (RA), marking substantial territorial gains for the early Islamic state.
– The Battle of Yarmuk, a decisive confrontation against Byzantine forces, played a crucial role in securing Muslim control over the region of Syria.
– For exams, note that Amr ibn al-As (RA) led the successful campaign resulting in the conquest of Egypt during this same period.