WI: Successful Arab siege of Constantinople in 674 triggers union of the former WRE?

Let's assume that the first Arab siege of Constantinople in 674-678 succeeds and the Caliphate manages to control most of Anatolia, pushing the Byzantine Empire into collapse.

Considering that the consolidation of Umayyad power in Anatolia and Thracia would have been pretty challenging and demanding, it would probably mean that IOTL Umayyad conquest of Africa (690s) would have been postponed.

So, the Byzantines could have the chance of reorganize themselves in the surviving Western part of the Empire: Africa, Sicily and Southern Italy (maybe part of Greece too, even if now Greece is dangerously exposed). However it is quite obvious that in this scenario the Byzantines would realize that they alone could not stop a further expansion of the powerful Caliphate once it would be ready for another push.

In such scenario, Byzantines should try to form a solid alliance with other Christian nations in order to keep the Arabs at bay, but none of the main candidates (Visigoths, Merovingian Franks, Lombards...) seem to be powerful enough unless all or most of them participate.

Could an alliance of West Byzantines, Visigoths, Merovingians and other Christian Germanic nations be viable at the late 7th century in order to stop the advance of the Caliphate in the Euromediterranean region?
 
Map with some ideas of the consequences:

Caliph_01.png
 
Honesty, the first Arab siege of Constantinople going for the Arabs is pretty hard. The Eastern Romans Navy is the Royal Navy of the time. Simply put, the EER Navy is the most well funded, most well trained, most well build, and outnumbering everyone else in the region. In OTL, the Arab Navy was destroyed. Besides, the Umayyada are overstretched as it was in OTL.

However, what we would see is Greco-Roman culture taking over the Arabs with the accelerate the fragmentation of the Umayyad Empire.


I've argued before that Arab expansion in the Balkans is likely to "soak up" the energies that IOTL went into conquering Africa and Iberia. Africa may well still be doomed in the long run, but I doubt it'll be conquered entirely until well into the eighth century, and Visigothic Iberia is quite likely to avoid Arab conquest altogether: major Caliph-sponsored military efforts are going to be directed towards the Bulgars and Avars.

It's fairly likely, I think, that you'll see the Exarchs of Ravenna trying to claim the imperial title shortly after the fall of Constantinople, backed by the Papacy, thus beginning a HRE of a sort generations earlier than OTL: an HRE that actually is a genuinely direct descendant of the late antique Roman Empire.

A conquest of the ERE (I'm assuming in the 670s, as I think the 710s are too late) is going to mean the Arabs continue to be heavily influenced by late Roman culture as they were historically in the seventh century. The later rise of Iranian influence may still happen, but in this case I can see it quite easily splintering the Arab Empire altogether, with a much stronger Graeco-Roman element within the Arab community.

Furthermore, the 670s is still a while before medieval Islam as we know it had properly developed: the failures of the earlier Arab leaders against the Romans were a major spur to Abd-al-Malik's proper foundation of a "Caliphate", so there'll definitely be butterflies here. The Arabs are still most likely going to be monotheists who venerate Muhammad and Allah, but they may have religious views and practises by the 750s that would have the Abbasid Caliphs of OTL recoiling in horror. Arab figurative art is one particularly obvious one I can see continuing, as well as perhaps shared places of worship.



I am not entirely sure on this one..... One issue the Umayyad will incur is the issue of massive amounts of non Semitic Christians who have previous loyalties covering their newly conquered land and then an extended border to be attacked. The Ottomans succeeded in the conquest of Greece, Bulgaria, Serbia, etc, not simply by might but they dominated Anatolia, the most important piece of the entire Byzantine Empire; without its Turcofication following the 900s-1200s, the conquest the Ottomans made, would be very unlikely and or weakly made.

For instance, the Umayyad for all its prowess, is going to be highly pressed on its various fronts, once expanded into Byzantium fully. Most especially, in the north, they will face the Khazar, Slavs and Bulgars. All of which will see this as an opportunity to attack or simply flee northward. Khazars for instance will likely be drawn into their wars with the Umayyad over the Caucus mountains and the Pontic Steppe regardless, increasing further the spread of Umayyad forces. Then, the Umayyad will conquer North Africa and perhaps Iberia shortly after and extend their borders immensely. The further possibility of a Khawarij revolt becomes more possible and prevalent, especially once you consider the vast numbers of people added to the Islamic world.

Frankly, this could lead to Islam being broken down even further. I actually can imagine a scenario whereby, Islamic states rule Iberia, Libya, Egypt, eastern Anatolia, Iraq, Arabia, Shams and possibly Sindh. This has Algiers, Morocco and parts of Tunisia breaking free from Umayyad rule by the Khawarij powers who likely then turn on each other, leading to a return to status quo in the area (likely to be conquered by Islamic states later/ as Indonesia was). Then, it becomes all the more likely for Greece to then transfer back to Christian powers or perhaps, Slavic or Bulgar states. This however, means that Aegean islands remain likely Muslim or Arab ruled, so that would include Crete, Cyprus, Rhodes, Corfu, etc... Then Iran could easily break off as was possible before the Abbasid Caliphate arose, whether this is a moderately Islamic state or Zoroastrian, who knows.
 

Brunaburh

Gone Fishin'
At this early date, is the Ankh-Morpork scenario not possible? Constantinople changes the Muslims more than the other way round.
 
If the Arabs take out the ERE in one scoop, they've effectively inherited their entire state and infrastructure. Considering the Roman language was used for much administration post-conquest IOTL, it's likely the elite eventually adopts it. Otherwise, they're overextended.
 
If it’s conquered quickly and then ruled, there’s a good chance of it breaking free, possibly even as a Christian state, upon Umayyad fragmentation.
 
"Christian" and "muslims" are going to be very different things here, one way or the other. Islams identity is still somewhat fluid, and given existing similarities... even otl, Christians erroneously described Islam as a heresy, ttl that might actually have some truth to it. I don't know enough about Islamic theology or early Islam to speculate but I suspect you'd see a sort of Sikh style fusion in whatever splinter state sets up shop in anatolia/greece with Greek taking over as the dominant language, much as Persian did in Iran (quite possibly extending into Syria or the Levant even).

In the long run it could see a mass conversion of the Balkans and Russians to Islam, much the same way that the Bulgars and Kiev were converted by Byzantine influence Otl.
 
An Arab success during the first siege is rather more unlikely than during the second one; nevertheless, assuming it somehow happened, it has a number of effects. First, it immensely strengthens the prestige of the Umayyad regime. Perhaps enough to avoid the Second Fitna, but given politics and rivalries within the Islamic community, probably not. It will however give the Umayyads a much larger powerbase during the civil war. How they make use of it depends on how Muawiya handles the capture of Constantinople; it is rather unlikely that he will move his residence there immediately, amidst a largely foreign population, and leave the relative security of Syria, but a settlement of the city as a military colony and some other such colonies in Anatolia and Greece would a) increase his own powerbase and b) be a good opportunity to move potential troublemakers to remote frontiers, where they will be too busy fighting off the infidel to challenge Umayyad rule. OTOH, it may weaken the Umayyads by removing some of their best and most reliable troops from Syria, at least during the crucial early stages of the civil war. Assuming the Umayyads emerge again victorious from any succession struggle, with a still unified caliphate (that's a rather big if, as IOTL), comes the second effect, namely that on the direction of Islamic expansion. IOTL, the Marwanid branch of the Umayyads that took power after the civil war showed a tremendous expansionist drive, taking North Africa, Spain, Transcaucasia, Transoxiana, and parts of northern India, in the period 690-740. ITTL, much of this energy will be directed into the Balkans and Italy instead, to secure Constantinople. IOTL, Umayyad expansion was somewhat haphazard, but here it will be focused onto that one objective, especially if the city becomes a caliphal capital. This will certainly be to the benefit of their long-term prospects, as they are less likely to disperse their efforts on the remotest corners of their empire. OTOH, the underlying tensions that ultimately undermined the Umayyad dynasty will not go away just like that, but no-one can really predict the knock-on effects from a 670s POD. No conquest of North Africa (and the rapid Islamization of the Berbers), or of Transoxiana and the eastern marches of Iran (with the resulting frontier societies that played such a decisive role in Islamic history), will certainly render the later Islamic world unrecognizable to an OTL observer. In the long term, a division between a Mediterranean-oriented and an Iran-oriented part of the Muslim world will happen (it did so, to a greater or smaller extent, and repeatedly, IOTL), but here it is likely to look even more like the old Roman-Persian dichotomy in a new Islamic guise, as these two cultures will also impact the respective areas, in contrast to OTL where Persianate culture was spread by the Abbasids and became the Islamic norm.
 
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