What's the relation between the Kushan Empire and the Sassanid Empire in Iran?
The Kushan Empire  was a syncretic empire, formed by the Yuezhi, in the Bactrian territories in the early 1st century. It spread to encompass much of modern-day territory of Uzbekistan, Afghanistan, Pakistan and Northern India. The Sasanian or Sassanid Empire officially known as Eranshahr  was the last Iranian empire before the early Muslim conquests of the 7th–8th centuries AD. Named after the House of Sasan, it endured for over four centuries, from 224 to 651 AD, making it the longest-lived Persian imperial dynasty.