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Welcome on board! I hope you'll enjoy it as much as we do.
In 460 Carthage and the coast of North Africa had been under Vandal control for quite some time and this had dramatically bad affects on the empire with the loss of grain.
More than the problem of grain (which was quite real after the mid-450's (it seems that Vandal had maintained the annonarian supply up to Valentinian III's death) it was the problem of fiscal revenues that were entierly captated by Vandals, whom relation with Rome was far more independent (if not hostile) compared to other Barbarians.
The eastern and western empires built a huge fleet to retake it. The invasion ended in disaster and fiasco with the Roman ships burning and the treachery of certain senators.
Treachery is a common trope of Roman defeats in the Vth century tough, and how they were commonly explained even in face of evidence sometimes.
What if the Roman's had retaken one of their most crucial provinces and crushed the Vandals in North Africa?
As Majorian took the (shared) lead of the WRE, things already went too far : he skillfully managed to play Barbarians against other Barbarians (as Aetius did in his time, which probably inspired Majorian) by forcing them into obedience but never crushing them as he depended from their military resources : in short, it was an expedient.
Even Roman troops were importantly Barbarized, Ricimer already having too much control on imperium to really accept a too powerful and too monarchical emperor, especially if he was more and more dependent from Constantinople : in the mid to late Vth century, WRE couldn't really stand on its own and was either to search ressources among Barbarians or in the eastern Roman state.
Don't get me wrong, a reconquest of Carthage could lead late WRE to survive longer than IOTL, but with ressources already depleted, but would wear it eventually and make it unable to undergo important reforms (as Majorian's demise points), either turning it into a patrician Italy acknowledged by Constantinople, either being swalloed up by eastern emperors that tought themselves being the only legit supreme authority (even during Majorian's reign).
We know Romans already, at this point, managed to take back some points, especially places where Vandalic power wasn't that certain, such as Tripolitania, so let's assume they continue their advance. Eventually, Vandals would be forced to negociate at sword-point, as the coalition couldn't be maintained eternally, and give up several territories and assets.
I think that the first to go would be territories losts or cut off from Vandals : Tripolitania, Corsica, Sardinia, Balearic Islands and Sicily. You certainly noticed that didn't mentioned Africa : well the goal of the expedition was to curb down Vandalic thalassocracy that allowed them to raid everything in sight, rather than reconquer Africa.
Eventually, giving the poor state of WRE at this point (if Majorian couldn't hope to hold Africa,
Athemius sure couldn't), it means that these regions would be de facto under control of Constantinople, makin
g the ERE having a more western foothold in the west in the coming decades, a bit like Dalmatia was in the same period.
Assuming Romans and their auxiliaries takes back Carthage and the "Vandalic sors", the lands in Proconcular Africa that Genseric directly took over (the rest of Africa being still under its direct authority but with fewer changes), you'd still have Vandals in the regions, probably pushed back in their short-lived foedus in Numidia : again, WRE depended on the presence of Barbarians in military matters. IOTL it only gave some time to WRE to die in its corner. It would ask, as pointed, a slightly different strategy that wouldn't be based on the acceptance of the loss of Africa, which predominated in the mid-Vth century tough, and more subsides from ERE.
It would have interesting consequences having central Romania being swalloed up by its eastern counterpart, tough : when Africa was reconquered by Byzzies in 535, and altough the Vandalic defeat was swift, Byzantines had a really bad view of Roman Africa's history at this point, mostly ignoring the relationship between Mauri and Africans that existed at least since the IInd century, causing a costly and not that stellar (for Romans) guerilla.
They, mostly wrongly, saw these kingdoms and tribal entities as invaders (mostly helped by the threat they represented as for what mattered the coastal population) rather than parts of the old system and actively searched to crush them ; the whole campaigns of Solomon is to be understood as a tentative to gain African to Byzantium and to get rid of what was seen as a foreign presence.
ERE having a better approximation of the local geopolitics would really help preventing the mistakes made in Africa, which led to decade of semi-guerilla warfare (and decades of neglects from the late VIth onwards) after having defeated Vandals, with (for exemple) allowing policies similar to Toglita's being adopted early on (and with more success).
But it would be an ERE reunifing most of Romania, rather than a surviving WRE being absorbated after a longer period of weariness.