Sentence:  "[W]e may surmise that there was a strong sense of Iranian unity lending solidarity to the eastern half of the empire. It is only in the generations after Alexander, in Eudemus and in Eratosthenes (ap. Strabo), that we find mention of the concept of a greater nation of <WSD>Iran</WSD> (Arianē) stretching from the Zagros to the Indus; but the sense of unity must have been there, for Herodotus tells us that the Medes were formerly called Arioi, and Darius I (followed by Xerxes) in his inscriptions proclaims himself an Iranian (Ariya) by race - he speaks of himself in ascending order as an Achaemenid, a Persian and an Iranian (Naqsh-i Rustam)." 
Meaning of the word marked with <WSD> tags:  regions inhabited by the Iranian peoples.