Sentence:  "Kavi means a king, but it is particularly used of the kings belonging to the second and most celebrated of the two mythical dynasties of <WSD>Iran</WSD>." / "One certain fact is the occurrence of geographical names [Bactria, Sogdiana, etc] in Vendidad I, which are obviously intended to describe the earliest homes of the Iranian races whose lore was the Avesta." 
Meaning of the word marked with <WSD> tags:  regions inhabited by the Iranian peoples.