Justinian I attempted to restore Roman Authority in Italy but it ended up in a fiasco when leading commander of the Roman Army, Belisarius, died in Ravenna. Even worse was when the Army morale broke and was targeted by ambushed by Goths and Lombards. The disaster of the campaign and continous hostility by both Ostrogoths, Vandals and Turkic Tribes around the Black Sea caused unmanagable pressure on the borders. By 700, the East Romans were merely a city of Constantinople at mercy of the Bulgars.
If Belisarius succeeded in reconquering Italy, would the East Roman Empire last longer? Would the Persian King convert to Christianity anyway?
Well, I do know this: the Goths and Lombards were not doing terribly well prior to Belisarius's death.
A more powerful empire in the Mediterranean would likely be able to hold off the Arab migrations about a century later. Unless the ERE did something really stupid like fight a decades long war with Persia, we probably wouldn't see the vast Jewish empires in Arabia and North Africa.
Maybe, but maybe not. Keep in mind that the migrations that occurred in Italy, at least, were mostly from
Christian Arabs-the Muslim Arabs did have a foothold in Sicily for a while, true(as well as in the south and west of Hispania) but most of the peasantry who stayed behind were converted to Christianity after the conquest of the Emirate of Sicily in the 11th century.
Also, in regards to the Jewish empires you're referring to-Samirah
is still a great cultural power, sure, that is true. And so were Yemen and New Judea at one point-but even Samirah isn't as large as it once was, though it still dominates much of northern Arabia and the Levant(yes, the Muslim states that emerged in the 7th century were very formidable opponents, but Samirah had, by the 11th Century, permanently secured the northwest of Arabia), and Yemen is only a minor power these days(with New Judea having been swallowed up by the Egyptian Empire in the 18th Century).
ASB. Even before Belisarius' death, the Eastern Romans had proven themselves unable to deliver a decisive defeat to the Ostrogoths. The Ostrogoths were just too popular in ITaly and their government was too well organized. Sorry, but there is just no way this could happen.
Yes, it
is true that the Ostrogoths were generally accepted back in those early days-but let's not forget that, after the Ostrogoths drove out the Eastern Romans, they did, unfortunately, become rather arrogant and eventually oppressive.....
which would lead to the Ostrogothic elite being driven out of the area altogether by the mid 8th Century. So perhaps an initial defeat at the hands of the Eastern Romans might well have lead to a better reality for the Ostrogoths in the long run.....
Besides, this would remove the Gothic Renaissance of the following centuries and that would likely lead the West to become a backwater.
I'm sorry, but this isn't
quite true. Yes, the surviving Visigoth realms did benefit significantly from the Europan Renaissance, but-contrary to the views of many Gothic Nations enthusiasts-they were not particularly special in regards to their contributions, any more than the Italian states or the Gallic kingdoms. And let's not forget that the surviving
Ostrogothic realms were actually quite backwards by that time(and a constant headache for the Polonians, Lithuanians, and the Rus' states alike!).
The only power which would be able to fill the vacuum would be the Franks and OTL shows just how much of a disunited wreck they were.
That much is true, though. There
is a reason why it took until the 13th Century for any real unity to occur in northern Gallia, much as it was for England until the end of the 10th century, and Hibernia in the late 16th.