What if the Byzantine Empire had an emperor that could achieve the conquests of Alexander the Great? How significantly would India and Persia have changed? Could this emperor (if at the appropriate time) contain the spread of Islam?
A Byzantine controlled Palestine would butterfly away the Crusades obviously. Perhaps the Crusades in reverse? Though Egypt would be Byzantine, too. If the POD is early enough, Islam may be butterflied away completely. Hopefully the Byzantines retain the knowledge amassed during antiquity if that is the case.
But that's basically having the Eastern Empire maintain its original borders, not repeat Alexander and conquer Persia. One possibility would be if the Romans weren't exhausted right before the Islamic conquest. Then perhaps they could attack the Arabs after they conquered parts of Mesopotamia and Persia, but before they could fully consolidate those conquests.
But that's basically having the Eastern Empire maintain its original borders, not repeat Alexander and conquer Persia. One possibility would be if the Romans weren't exhausted right before the Islamic conquest. Then perhaps they could attack the Arabs after they conquered parts of Mesopotamia and Persia, but before they could fully consolidate those conquests.