For all practical purposes they lived in a truck stop a little off the main routes of Persian conquest.
After the Dark Ages got rolling, and enough people had died of plagues and famine, this group became relatively powerful ~ on the other hand, it wasn't until they began hiring unemployed Byzantine legions that they got a real hang of conquering stuff.
They then threw the Persians out of everywhere West of the Euprhates much to the applause and relief of everybody else.
Now, about the Persians ~ the dominant language is part of the Indo-European family. On the other hand, those early Indo-Europeans were so few in number they left behind little, if any, genetic heritage. For all practical purposes almost all the peoples in today's Iran and Iraq are part of the same ethnic group. Part speaks modern Arabic. Part speaks modern Farsi. Otherwise, all same thing.
That is not true. As a Persian who has visited Iran and seen tens of thousands of both Iranians and Iraqis there no similarity. Iranians have fair skin with more square faces and higher cheek bones the Iraqis are generally much darker with more oval faces and lower cheek bones. I can spot a Persian from an Iraqi about 95% of the time.