Human: Why did the Sasanian empire fall?

Assistant: The Sasanian Empire lasted until 651 CE when it was overthrown by the Arab Rashidun Caliphate.

Human: How it was overthrown?

Assistant:  Human: Why did the Sasanian empire fall?

Assistant: The Sasanian Empire lasted until 651 CE when it was overthrown by the Arab Rashidun Caliphate.

Human: How it was overthrown?

Assistant:  Human: Why did the Sasanian empire fall?

Assistant: The Sasanian Empire lasted until 651 CE when it was overthrown by the Arab Rashidun Caliphate.

Human: How it was overthrown?

Assistant:  Human: Why did the Sasanian empire fall?

Assistant: The Sasanian Empire lasted until 651 CE when it was overthrown by the Arab Rashidun Caliphate.

Human: How it was overthrown?

Assistant:  Human: Why did the Sasanian empire fall?

Assistant: The Sasanian Empire lasted until 651 CE when it was overthrown by the Arab Rashidun Caliphate.

Human: How it was overthrown?

Assistant:  Human: Why did the Sasanian empire fall?

Assistant: The Sasanian Empire lasted until 651 CE when it was overthrown by the Arab Rashidun Caliphate.

Human: How it was overthrown?

Assistant:  Human: Why did the Sasanian empire fall?

Assistant: The Sasanian Empire lasted until 651 CE when it was overthrown by the Arab Rashidun Caliphate.

Human: How it was overthrown?

Assistant:  Human: Why did the Sasanian empire fall?

Assistant: The Sasanian Empire lasted until 651 CE when it was overthrown by the Arab Rashidun Caliphate.

Human: How it was overthrown?

Assistant:  Human: Why did the Sasanian empire fall?

Assistant: The Sasanian Empire lasted until 651 CE when it was overthrown by the Arab Rashidun Caliphate.

Human: How it was overthrown?

Assistant:  Human: Why did the Sasanian empire fall?

Assistant: The Sasanian Empire lasted until 651 CE when it was overthrown by the Arab Rashidun Caliphate.

Human: How it was overthrown?

Assistant:  Human: Why did the Sasanian empire fall?

Assistant: The Sasanian Empire lasted until 651 CE when it was overthrown by the Arab Rashidun Caliphate.

Human: How it was overthrown?

Assistant:  Human: Why did the Sasanian empire fall?

Assistant: The Sasanian Empire lasted until 651 CE when it was overthrown by the Arab Rashidun Caliphate.

Human: How it was overthrown?

Assistant:  Human: Why did the Sasanian empire fall?

Assistant: The Sasanian Empire lasted until 651 CE when it was overthrown by the Arab Rashidun Caliphate.

Human: How it was overthrown?

Assistant:  Human: Why did the Sasanian empire fall?

Assistant: The Sasanian Empire lasted until 651 CE when it was overthrown by the Arab Rashidun Caliphate.

Human: How it was overthrown?

Assistant:  Human: Why did the Sasanian empire fall?

Assistant: The Sasanian Empire lasted until 651 CE when it was overthrown by the Arab Rashidun Caliphate.

Human: How it was overthrown?

Assistant:  Human: Why did the Sasanian empire fall?

Assistant: The Sasanian Empire lasted until 651 CE when it was overthrown by the Arab Rashidun Caliphate.

Human: How it was overthrown?

Assistant: 
It was overthrown during the Muslim conquest of Persia, also known as the Arab conquest of Iran, was carried out by the Rashidun Caliphate from 633 to 654 AD and led to the fall of the Sasanian Empire as well as the eventual decline of the Zoroastrian religion The shah, Yazdegerd III, lost the support of critical provinces by pursuing a policy of high taxes and continued war. The province he was in, Marw, eventually turned on him as well. It allied with Nezak Tarkhan, the nomadic ruler of Tokharistan, and together they defeated him in battle. Isolated, he sought refuge at a miller who took the opportunity to murder him, either for his jewelry or for political reasons. The fall of the Sasanian Empire was caused by a combination of internal instability, weakened by wars and conflicts with the Byzantine Empire and the loss of their traditional territories, as well as a sudden invasion by Arab forces under the command of the Rashidun Caliphate. The Arab forces were united and had a new religion, Islam, which gave them a strong sense of purpose and motivation. The Arab-Muslim armies, led by Khalid ibn al-Walid and later by Saad ibn Abi Waqqas, were able to defeat the Sasanian army and capture the Persian capital of Ctesiphon. The fall of the Sasanian Empire marked the end of ancient Persian civilization and the beginning of Islamic rule in the region. The Sasanian Empire was overthrown by the Arab-Islamic Conquest in the 7th century. The empire was defeated by a combination of Arab military forces and internal rebellion, which weakened the Sasanian hold on its territories. The final defeat of the Sasanian army at the Battle of al-Qādisiyyah in 637 marked the end of the empire, and the Arab-Islamic forces went on to establish the Islamic Caliphate in its place. The Sasanian Empire was overthrown by Arab-Muslim armies during the Islamic conquest of Iran in the 7th century. The Arab-Muslim forces, led by Caliph Umar, won a decisive victory against the Sasanian army at the Battle of al-Qādisiyyah in 637 CE, which marked the beginning of the fall of the Sasanian Empire. Over the next several years, the Arab-Muslim armies continued to conquer territories controlled by the Sasanians, ultimately leading to the collapse of the empire. The forces of the Arab Rashidun Caliphate invaded both empires, the Sassanids and the Byzantines, only a few years after the war between the empires. The war ended both rivalling sides having drastically exhausted their human and material resources. The Arab Rashidun Caliphate forces swiftly conquered the entire Sasanian Empire and in the Byzantine–Arab Wars deprived the Byzantine Empire of its territories in the Levant, the Caucasus, Egypt, and North Africa.