Military expansion. The Rashidun Caliphate expanded gradually; within the span of 24 years of conquest, a vast territory was conquered comprising Mesopotamia, the Levant, parts of Anatolia, and most of the Sasanian Empire. Unlike the Sasanian Persians, the Byzantines, after losing Syria, retreated back to Anatolia.
1 And the nature of this reality again can neither be consistently represented as a fixed and hard substance nor as an unalterable something, but only as a fixed order of recurrence of continually changing events or impressions.
C2 Someone who is persistent continues doing something or tries to do something in a determined but often unreasonable way: Be persistent - don't give up. He has been a persistent critic of the president. She is a persistent offender and has been arrested five times this year for shoplifting.