WI: Arab Caliphates only attack the Sassanids/Eastwards, not the ERE?

[History Learner]

While doing some reading on early Islam, I found out Muhammad had actually sent out letters to the various polities that surrounded Arabia (and some within) seeking to convert them to Islam. Of particular interest to me was the letters sent to Emperor Heraclius of the Eastern Roman Empire, and the associated Islamic story of his response:

In contrast to Khosrau II, who had been sent a similar letter earlier, the Byzantine Emperor Heraclius kept the letter and sought to find confirmation concerning what it contained. This is quite different to the treatment accorded to his letter to Khosrau II of the Sassinid Empire. According to Abdullah ibn Abbas, the latter was sent with Abdullah ibn Hudhafa al-Sahmi by way of the Governor of Bahrain.​

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“So, when Khosrau read the letter he tore it up. Saeed ibn al-Musaiyab said, ‘The Prophet then invoked God to destroy and disperse Khosrau and his followers fully and with severity”. (Saheeh Al-Bukhari)​

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The Sassinid Empire was to utterly dissolve almost immediately, first through the defeat by the Romans, and then by the onslaught of the new Muslim nation. The Byzantine Empire, too, while still under Heraclius, dissolved in Egypt, Palestine and Syria. However, unlike the Sassinid Empire, the Byzantine Empire continued on in various forms for another 800 years until Constantinople finally fell, and this may be because of the contrast in the way each of the letters was received.​

Wikipedia alleges the following, but I've been able to find any corroborating evidence:

According to Muslim tradition, the letter was sent through Abdullah as-Sahmi[a][10] and after reading it Khosrow II tore the document,[14] saying, "A pitiful slave among my subjects dares to write his name before mine"[11] and commanded Badhan, his vassal ruler of Yemen, to dispatch two valiant men to identify, seize and bring this man from Hejaz (Muhammad) to him. When Abdullah ibn Hudhafah as-Sahmi told Muhammad how Khosrow had torn his letter to pieces, Muhammad is said to have stated, "May God [likewise] tear apart his kingdom," while reacting to the Caesar's behavior saying, "May God preserve his kingdom."[15][10]​

So, taking this as accurate, what if the coming Arab expansion had been targeted at Sassanid Iran, leaving aside the Eastern Romans? It could be justified both based on this interaction as well as the fact the ERE is Christian (People of the Book), while the Sassanids are "Pagan Fire Worshippers".

 

[WolfBear]

I wonder if we could see deeper earlier Islamic penetration into places such as India in this TL to compensate for their lack of expansion to the West. The West would remain a Christian zone in this TL, with the Mediterranean Sea remaining a Christian lake. I would presume that having the Muslims conquer China would be a step too far, right? Though I do wonder just how far north in Central Asia they would be capable of going earlier on. Siberia I would presume would be difficult to access due to logistics and also because there is nothing of value there at this specific point in time, right?

I wonder if we could see Caucasian groups such as the Chechens Islamized much earlier in this TL.

 

[History Learner]

I wonder if we could see deeper earlier Islamic penetration into places such as India in this TL to compensate for their lack of expansion to the West. The West would remain a Christian zone in this TL, with the Mediterranean Sea remaining a Christian lake. I would presume that having the Muslims conquer China would be a step too far, right? Though I do wonder just how far north in Central Asia they would be capable of going earlier on. Siberia I would presume would be difficult to access due to logistics and also because there is nothing of value there at this specific point in time, right?

I wonder if we could see Caucasian groups such as the Chechens Islamized much earlier in this TL.

Further Islamic advance into India is exactly why I put "Eastwards" in the title, as I see it as a likely ramification of this PoD. The Afghans probably get converted sooner, while the Caliphate not needing to control the Levant and Egypt means they can take and Islamify Punjab, Rajasthan and Sindh; credit to @Ricardolindo for bringing this possibility to my attention. This would serve as a pull factor for the Turkic migrations out of Central Asia, as India is wealthy, closer and there is the ability to do Jihad via conquest of Hindu polities.

As far as the Caucasus, one idea going through my head is that the Arabs are not going to need to be as light handed in administration in Iran as they historically were forced to; there's enough Arab soldiers to settle elsewhere and exert direct control rather than bring in lots of ex-Sassanids into the fold. As a result, Iran probably is Islamified faster, and is more Arabized too culturally; there will likely be no Shia Islam ITTL. I'd imagine this will provoke earlier and stronger revolts by the Iranians, which could create a flux of refugees that would serve to help fortify Zoroastrian holdouts like the Dabuyids. Christian refugees, with support from the ERE, probably can secure Caucasian Albania. The Khazars, in my estimation, would thus be likely to go Nestorian, both due to Iranian Christians having influence, but also do to the specific strategic situation; the Romans are far stronger than historically, which means Christianity is stronger, but Nestorianism allows the Khagans to limit Constantinople's influence.

 

[WolfBear]

Further Islamic advance into India is exactly why I put "Eastwards" in the title, as I see it as a likely ramification of this PoD. The Afghans probably get converted sooner, while the Caliphate not needing to control the Levant and Egypt means they can take and Islamify Punjab, Rajasthan and Sindh; credit to @Ricardolindo for bringing this possibility to my attention. This would serve as a pull factor for the Turkic migrations out of Central Asia, as India is wealthy, closer and there is the ability to do Jihad via conquest of Hindu polities.

As far as the Caucasus, one idea going through my head is that the Arabs are not going to need to be as light handed in administration in Iran as they historically were forced to; there's enough Arab soldiers to settle elsewhere and exert direct control rather than bring in lots of ex-Sassanids into the fold. As a result, Iran probably is Islamified faster, and is more Arabized too culturally; there will likely be no Shia Islam ITTL. I'd imagine this will provoke earlier and stronger revolts by the Iranians, which could create a flux of refugees that would serve to help fortify Zoroastrian holdouts like the Dabuyids. Christian refugees, with support from the ERE, probably can secure Caucasian Albania. The Khazars, in my estimation, would thus be likely to go Nestorian, both due to Iranian Christians having influence, but also do to the specific strategic situation; the Romans are far stronger than historically, which means Christianity is stronger, but Nestorianism allows the Khagans to limit Constantinople's influence.

Any chance of the Byzantine Empire itself accepting a lot of non-Muslim Persian refugees in order to strengthen itself at its enemies' expense? In the book Romanland, it states that the Byzantine Empire was sometimes willing to accept refugees from enemy countries into its military, et cetera so long as they were willing to successfully assimilate.