After the fall of Rome starting from the Third century Imperial crisis,Smaller Germanic kingdoms took shape and mostly with their version of Authoritarian Christian Kingdoms. Say after the West Germanic/Nordic/Gothic conquest of the Western Roman Empire,an Emperor soon devices an idea for a well planned Classical religion to unify the WRE and also with the ERE and venture into lands that Alexander had gone into before. So this emperor now has an ethnic cum universal religion and a Monotheistic cum Polytheistic religion built and adopts it. After beginning from his Frankish/Saxon/Gothic/Nordic hometown in some city like Lyon,Milan, Augsburg,Cologne or something like that,he conquers France,Germany,Italy,Britain and Spain with ease with newly devised strategies. Rome is made capital once again and once again,Mediterranean looked like becoming a private lake. He fixes all the philosophy and science schools and established many of them along the coast of His Mediterranean prize. North Africa falls soon enough. WRE is revived. He adopts elements from Hungarian,Roman,Celtic and Germanic religions in this new exotic religion and the WRE is surging up again. He now goes into the Constantinople for a visit. He gets states admiring him for his fit and tall physique and gets admiring comments all the way till the palace next to the under construction Hagia Sophia. He now speaks privately to the Byzantine Emperor that we will support each other like the old Rome with grains shipping from Egypt and Syria and German/French or Italian students studying at Athens and Greek and Syrian students at Massalia/Tolosa or Rome. He convinces the emperor of this new religion that has good and useful parts of Christianity and gets acceptance.
Now how does this revived Rome in around 550-640CE fare? Arab Muslims would now be crushed and the tide would be reversed with Arabia converting to the Roman Empires religion and becoming a vassal. Armenia could be incorporated. Persia could quiver and submit. Slavs and Caucasians also willingly join. How much wonders could Europeans achieve under this empire? How would other regions be influenced from this? If Persia is now by their side,that could affect even parts of India and the Sogdians and Tocharians could also get influenced. How would the world fare with this Huge Rome in place? Tell all your opinions.