Muslim conquest of Persia

• 1. The Fractured Empire

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  In the year 628, the Sasanian Shah Khosrow II was executed. His death triggered a rapid collapse of political stability across Persia. Within four years, ten new royal claimants were enthroned in succession. The empire fractured into competing factions while the army remained exhausted from decades of war against Byzantium. A large-scale civil war known as the Sasanian Interregnum began that same year and resulted in government decentralization by 632. This internal chaos left the state vulnerable to external threats it could no longer effectively resist.

• 2. Battles That Shattered Borders

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  The first major invasion of Sasanian territory occurred in 633 when Rashidun forces conquered parts of Asoristan. Khalid ibn al-Walid led this initial campaign with an army of 10,000 volunteers. He defeated Persian forces in four consecutive battles during April and May of that year. By June, he laid siege to Al-Hirah which surrendered in July. The second invasion began in 636 under Sa'd ibn Abi Waqqas. At the Battle of al-Qadisiyyah, his forces defeated the main Persian army within three months. This victory ended all Sasanian control west of modern-day Iran. The final decisive engagement took place at Nahavand in December 642 where Muslim commanders destroyed a force of 100,000 veterans recruited by Yazdegerd III.

• 3. Revising The Historical Record

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  Traditional Western accounts relied heavily on Armenian bishop Sebeos and later Arabic chronicles for their understanding of these events. Parvaneh Pourshariati published a groundbreaking study in 2008 titled Decline and Fall of the Sasanian Empire. Her research challenged the conventional timeline suggesting Arab conquests began between 628 and 632 rather than after 632. She argued the Sassanian Empire functioned as a decentralized confederation with powerful Parthian families retaining significant independence. These northern and eastern Parthian clans withdrew to their strongholds making peace with Arabs instead of fighting alongside the central Sassanian authority. This internal fragmentation meant the empire was ill-prepared to mount a cohesive defense against invading forces.

• 4. Taxes And Administrative Continuity

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  Under Umar ibn al-Khattab's rule, the new administration retained much of the existing Sasanian bureaucratic structure. Provinces were called ustan while districts became shahrs centered upon capitals known as shahristan. Non-Muslim subjects paid a special tax called jizya calculated at varying rates usually two dirhams for able-bodied men. Women and children remained exempt from this tribute. The old land tax known as Kharaj was also adopted by the conquerors. Official language policy shifted over time; Middle Persian remained the administrative tongue during the Rashidun Caliphate until Al-Hajjaj ibn Yusuf changed Iraq's official language to Arabic in 714. This transition marked the first reinstatement of a Semitic language in Mesopotamia since the Neo-Babylonian Empire fell in 539 BC.

• 5. Centuries Of Religious Change

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  Zoroastrianism had been the official religion of Persia since circa 550 BC under the Achaemenid Empire. Following the conquests, Zoroastrians faced execution or enslavement if they refused conversion. Those who paid jizya were subjected to humiliation and ridicule by tax collectors. Conversion offered freedom to slaves captured in war but mass conversions did not occur immediately. The process stretched over many centuries with a majority of Persians still following Zoroastrianism at the turn of the millennium. By the late 10th century most Persians had become Muslim while Sunni Islam dominated until the Safavid dynasty forced conversion to Shia Islam in the 16th century. Many Zoroastrians fled eastward to India where kings accepted them as refugees.