In the early 600s, Arab armies, under the First Caliphate, overwhelmed the Sassanid Empire of Persia, conquering everything in their path- in the east. However, the Byzantine (East Roman, I suppose is the official name) Empire, though nearly as war-weary as Persia, managed to keep the Arabs out of their land.
Christianity would likely not be the majority religion of Africa today... and since areas like Mesopotamia became Arabic in culture after the invasion, might the same thing happen to Egypt (maybe a bit far-fetched, Egypt has so many people after all) or the Holy Land? What would Islam look like with more Christian influence? What about Greece- I don't think the Caliphate was well known for it's navy...
Christianity would likely not be the majority religion of Africa today... and since areas like Mesopotamia became Arabic in culture after the invasion, might the same thing happen to Egypt (maybe a bit far-fetched, Egypt has so many people after all) or the Holy Land? What would Islam look like with more Christian influence? What about Greece- I don't think the Caliphate was well known for it's navy...