WI: Sassanian-Tang alliance reconquer Persia from the caliphate?

After the exiled Persian king Peroz III died in China in 679, his son Narseh was given an army by the Tang emperor to reconquer Persia. The project failed, the Chinese army stopped after retaking the Tarim basin and Narseh was unable to rally the Persians to his cause.

But what if the reconquest was successful? Persia returns to Zoroastrianism and native rule? Islam never dominant in Central Asia, India, and South East Asia? An Lusan Rebellion butterflied away? Longer lasting Tang dynasty and outward looking China? Intermarriage between Persian and Chinese royalty? Alliance against the caliphate with the Byzantine empire?

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Hmmm...it's certainly possible but I think it requires a rather early POD...

The number one fix is making sure the Sino-Persian detachments don't waste resources fighting the Gokturks and instead ally with them. After that, there are a great deal of alternatives to either increase the loyalty of the Persians to Zoroastrianism and the Sassanids or to nerf the Arabs. For the latter, a stronger Byzantium is probably the best option; a Byzantine victory at Yarmoulk might halt their westward offensives and give Byzantium a good position to invade Arabia if it looks like the Caliphate is struggling against the Persians/Chinese. Even still, I think you'd have to build more popular loyalty to Zoroastrianism or equivalent. A mass conversion to Manichaeanism might work, though Islam, being much less ascetic, would still appeal to many Iranians. Perhaps Mazdakism is incorporated into the faith by an earlier Shahanshah building up more popular attachment to the old religion?

Alternatively, earlier and stronger Muslim persecution of the Zoroastrians could well do the trick.

As for the impacts, well, the Turks likely never convert to Islam in this scenario. Indeed, if the Romans manage to recover Syria/Palestine/Egypt ITTL, Islam might well become an Arab national religion only. It is likely that the Turks are heavily Persianised ITTL. Likely Sassanid Persia and China compete for influence in Central Asia; Manichaeanism or Zoroastrianism catch on among Sassanid-aligned tribes, and Buddhism or traditional Chinese faiths among the Chinese ones, though it is also possible for Tengriism to remain a much larger religion than IOTL.

Islam likely becomes the religion of the Arabs and the Arabian peninsula remains unified, since neither Rome nor Persia will have the ability to expand after their recovery. The Arabs likely move south, and establish trade networks similar to IOTL across the Indian ocean.