How did the Persians become a nomadic empire?

The Persians were never a nomadic empire. The Persian Empire was one of the largest empires in history, spanning over 5,500,000 square kilometres at its peak. It was founded by Cyrus the Great in 559 BC, and lasted until the Muslim conquest of Persia in the 7th century AD. The Persian Empire was centered in present-day Iran, and also included Mesopotamia, Syria, Egypt, Asia Minor, and parts of Central Asia and the Caucasus. The Persians were a highly advanced civilisation, and their empire was one of the most powerful and influential in history.