Correct. The origin of Indo-Iranians is found in what is now the Kazakh Steppe/Euroasian Steppe and most of them were nomadic like all cultures originally. Very few of them were settled. Not until they reached the Iranian plateau and encountered the remains of the Elamites and the Semites did they settle. For example even Cyrus the Great was heavily influenced by us Semites. He made Aramaic a Semitic language the official language, copied the rule of governance from the Semitic Assyrians, the symbols etc.
Andronovo culture - Wikipedia, the free encyclopedia
Read more here above.
At that time most if not all Semitic people were already settled. The only reason why certain Arabs - the Bedouins were force to become nomads (Bedouins) was because of the sudden climatic changes in parts of what is today Eastern Syria, Western (what is now the Syrian Desert) and Southern Iraq and Northern and Southern Arabian Peninsula.
Just 6000-8000 years ago the Arabian Peninsula was a lush and tropical place. Today only pockets of that once tropical fauna remains in the Southern provinces of KSA, Hijaz, Yemen (which is fertile land to this day) and Oman. No other place in the Middle East is tropical as those places. Banana, tea, coffee (which was first cultivated there and drunk - Sufi monasteries in 15th century Yemen) etc. is still cultivated there to this day. The monsoon rains are also affecting those areas.
This is why you have World UNESCO Heritage sites and wonderful architecture buildings in Mada'in Saleh in KSA, Petra in Jordan in valleys in desert/steppe like (although mountainous and rocky "desert" = Wadi Rum) today. Because of the climatic changes. No nomadic civilization on earth could make such marvels under such climatic conditions hence why you are unable to see such things anywhere on earth where the climatic conditions are not for that.
Anyway today step by step, after the desertification work etc. is being done large parts of Northern KSA are turning back to their origin = greenery.
No other place have such climate in the Middle East. The closest are parts of the coastal regions of Iran along the Caspian Sea.