The Arab Islamic conquests of the seventh century were of the same magnitude as the Persian conquests of 500 BC, Macedonian’s of 300 BC, Rome’s in 100 BC and Sassanians of 200 CE. The united and faithful barbaric tribes of Arabia were able to defeat two glorious civilizations of Persia and Byzantine, and took over an immense empire stretching from Morocco to India. The Arabic language grew from a limited Semitic tongue to dominate the Middle East, and Islam reshaped the Eastern cultural and religious outlook.
Sadly, western Iran was decimated by the Arab invasion, but the Persian culture survived in the Eastern provinces (especially Khorasan), where there was less resistance from the general populace and the Parthian minded nobility. Khorasan soon became the cradle of a new version of Persian identity and language (Farsi), as well as an independent military and political power.
The vicious internal Arab power struggles, which quickly assassinated 3 of the 4 original Muslim caliphs (Rashedin) and created the Sunni-Shia schism, enabled the independent minded Iranians to rapidly play a determining role in the Islamic Empire. In 750 CE, the Khorasan garrison rioted and lead by Abomuslim Khorasani, defeated the Umayyad caliph in Baghdad and brought their rivals (the Abbasids) to power. This victory initiated the dominance of Farsi governments in Khorasan, including the Taheri, the Safari, the Bueyeh and finally the Samanians.
The Taheri rule (810 CE) was a governorship well under the Caliph of Baghdad, but the Bueyeh actually conquered Baghdad and turned the Caliph into their puppet (year 945). The Samanians built a completely independent nation in Khorasan, where the Farsi language and culture flourished, and provided the bedrock for a distinct Iranian identity that has survived to this day. The Samanian kings were avid supporters of the Farsi identity, and supported such Iranian poets as Rudaki and Daghighi.
Despite their cultural and political greatness, the Samanian kings as well as the Abbasid caliphs soon became inundated with a massive migration of the Turkish tribes from Central Asia. Those Turks, who first enrolled their armies in the services of the Farsi and Arab kings, through their physical and character merits, subsequently took over the governance of the entire Middle East!
Influenced by the Samanian Farsi society, the new Turk rulers surprisingly maintained an avid support for the Farsi culture and their method of government (Viziers and Dabirs). The Ghaznavi Turks overthrew the Samanians in 1,005 CE and established a powerful empire in central Asia. They quickly converted to Sunni Islam, adopted Farsi as their court language, and provided a magnificent support to such Iranian luminaries as Beeroni, Farrokhi, Manuchehri and Ferdowsi.
It should be noted that the ‘new Turkish blood’ not only infiltrated and strengthened the Arabic and Persian nations, but also influenced the growth of the Jewish faith in Euro-Asia. After conversion to Judaism, a major Turkic tribe (the Khazars) established a new key Jewish state in Eastern Europe, which later on, significantly contributed to the Ashkenazi population in Russia, Poland and Germany.
The Turkish waves of invasion, from Central Asia, did not cease. The Seljuk Turks took over Khorasan and Iran, and then even captured Baghdad in 1,055 CE. They too became Sunni Muslim and very Farsi oriented, with most of their bureaucrats and Viziers chosen among the Iranians. Amazingly, the Seljuk even exceeded the Ghaznavi in their support of the Farsi culture, and cultivated such luminaries as Anvari and Khayyam. Their legendary vizier (Nezam-al-molk) created the first Iranian universities (Nezamieh). The Seljuk kings soon dominated the Muslim world with an empire stretching from central Asia to Arabia, and later became the forefathers to the Ottoman Empire.
The main challenge to the Seljuk rule came from the Shia Arab rulers of Egypt (the Fatimid), who opposed both the Sunni Caliphs of Baghdad, and the domineering Turks of Iran. The Fatimid established a network of supporters in Iran, the Esmaeli, who soon developed a viciously militant tactic and became famous as the Hashashin (Assassins).
That Shia-Sunni rivalry decimated the Seljuk government, as the Esmaeli established themselves in several formidable castles (including Alamot) and spread fear and terror throughout Iran. Their biggest ‘achievement’ was the assassination of the Iranian vizier (Nezam-al-molk) in 1092 CE, which escalated into a series of instabilities and wars of succession among the Seljuk.
The destabilized Seljuk princes fought one another and the Esmaeli for decades, causing widespread destruction of the cities and populace. Finally, another warlike Turkish tribe from Central Asia (the Khwarizmi) exploited the Seljuk/Esmaeli conflict and fought their bloody way into the Iranian plateau. The Khwarizm Shah briefly (1210 to 1220) ruled over a decimated country with weakened resources and scarce manpower. A great misfortune was that the widespread Iranian and even Muslim discord and internal blood-shedding coincided with an unprecedented Mongol unification and revival.
Many scholars consider the period prior to 1,220 CE as the Golden Age of Persia and even the golden age of Islam. At that time the Persian and the Abbasid culture, science and arts established themselves at such a magnificent plateau that none of the contemporary nations of the world could rival it. Moreover, the grand achievements of that period carried over to Europe (through the crusades period) and caused a global influence over the entire humanity’s development.
As examples, the philosophical and medical works of Avicenna were taught in the European universities until the 19th century. The mathematical contributions of Khayyam and Khwarizmi became the cornerstone of modern mathematics and astronomy. Furthermore, the literary contributions of Ferdowsi, Rudaki and Sadie established our distinct Farsi identity to this day.
Reference: The Golden Age of Persia , by Professor Richard Frye.