The caliph who was running the Arab conquests at that time was also one of those rare geniuses from Moslem history; he planned the entire set of campaigns that conquered Iran, and never left his dining room. But it’s also true that the Byzantines had been getting the better of the Sassanids, and that kinda knees the groin of the “died in the plague” school of thought regarding the decline of the Byzantines. Had they joined forces, the Sassanids and Byzantines might have stopped the Muzzie cutthroats at some battle in Mesopotamia. They did not, or could not, and then it became a piecemeal conquest.
>>>”The Sassanids exhausted themselves fighting the Byzantines and were conquered by the Arabs in an astonishingly small period of time.”
While this is true, I also think this is a rather one dimensional and simplistic view of how & why the Bedouin Arabs defeated the Sassanids. There were definitely other important contributing factors to the fall of the Sassanid Empire.
I recommend reading this book:
Shadows in the Desert: Ancient Persia at War (General Military)
http://www.amazon.com/Shadows-Desert-Ancient-General-Military/dp/1846031087
Also see “Customer Reviews” in the above link.
Other related readings:
Genocide of “Zarathushtis” (”Zoroastrians” in Iran)
http://ahura.homestead.com/files/GENOCIDEofZarathushtiesWEBJULY07_2_.pdf
History of Jihad against Zoroastrians of Iran:
http://historyofjihad.org/persia.html
P.S. – I often read and hear about how “Arabs” contributed so much to “Islamic” Architecture, literature, poetry, paintings and generally what has been coined as the “Islamic Civilization” particularly in the middle ages in the ME and North Africa (even in Southern Spain for instances). This view is often highly distorted, misrepresented and inaccurate.
Persians, Egyptians and North Africans (Carthagians i.e. current Tunisians) all had cultured and civilized pre-Islamic pasts. When the mentioned nations, particularly Iranians, were militarily defeated and, in many instances, forcibly converted to Islam, they brought in cultured traits and a tradition of learning into Islam.
In fact, the first codified grammar of Arabic was written by a Persian. The Arabs were unlettered, Mohammed himself was completely illiterate, in addition to being cruel, cunning and ruthless.
Therefore, the much vaunted Islamic Renaissance & Golden Age was, in essence, a renaissance of the Persian (Zoroastrian) converts to Islam beginning during the second Arab rulers of Iran [Abbasiad Caliphate].
During the first four caliphs Abba (Abu) Bakr, Umar, Uthman and Ali (the last three who were murdered by other Muslims in cold blood) and the Ummayad caliphate (the first Arab rulers of Iran) at Damascus and Iraq, there was no such thing as the Islamic Renaissance.
It was the Persians, North African and Egyptian converts who had a pre-Islamic legacy of being civilized, which they carried forward after being converted to Islam. In fact, Islam attempted to smother all pre-Islamic legacy of culture and civilization, and so it was only after the initial flush of Islamic savagery had passed over, that the newly converted people could - after a generation or so - pick up the threads of a civilized life.