The Persians believed that they were blessed by Ahura Mazdā, the supreme uncreated and benevolent deity of wisdom in Zoroastrianism, and that their religion and civilization were eternal. But their world came to an abrupt end in 651 AD, when the last Persian Empire, led by the Sassanid dynasty, was conquered by Arab invaders.
Yazdegerd III, the grandson of Khosrow II, was the last Sassanid Shah. After the death of Khosrow II, a succession of weak rulers had acquired the Empire’s throne. Almost every ruler was murdered within a year of taking power. The imperial palace had turned into a zone for slaughtering the kings and aristocrats. Generals had become warlords. They were commanding their own militia and battling for power all over the country.
In 632 AD, when Yazdegerd ascended the throne, he was eight years old. The real power was being wielded by his generals and the members of the aristocracy who were engaged in fighting the civil war. Overtaken by political intrigues and the civil war, the Sassanids failed to take note of the new threat: an army of Islamic Arabs. They did not expect an attack from the Arabian desert. But the unthinkable happened.
In 633, the Sassanid army was defeated by an Arab Islamic army near the Sasanian city of Hira. After the fall of Hira, the Persian elite started taking note of the Arab army. But by now it was too late. From 633 to 637, the Arabs defeated the Sassanid army in two major battles—Battle of al-Qadisiyyah and the Battle of Nahavand—and a series of smaller battles.
In 642, Yazdegerd fled to Isfahan where he tried to make a last stand by raising a small army. His army mutinied when the Arab leadership bribed the soldiers with the offer of free land. Yazdegerd fled to Estakhr but the Arabs invaded the city and razed it to the ground. The Persian nobles who had fled with Yazdegerd were killed in Estakhr. Yazdegerd ran from one city to another while being pursued by the Arab army.
In 651, Yazdegerd was hiding in the establishment of a miller in a small village called Marw. According to historical sources, the miller killed Yazdegerd for his jewelry. With the death of Yazdegerd, the age of Zoroastrianism in Persia came to an end. Islam became Persia’s state religion, and the Zoroastrians were given the dhimmi status. By the tenth century, there were very few Zoroastrians left in the country.