I subscribe to the idea that mohammad was a great conqueror. That much is clear. I also think it's reasonable that he saw what happened to empires once their leaders (in this case him) died. They were broken up and conquered by someone else.
His rather absurd religion does a good job of keeping the empire together (convert, pay a “tax”, or die).
I don't know if you're arguing that islam is somehow a legitimate religion in the same way that Christianity or Judaism is legitimate, but I don't buy that idea. It's clear - by their actions - that muslims are lacking in a variety of areas. Their actions speak so loudly that I can't hear a word they're saying. Kind of like obama. Actually, A LOT like obama.
Mohammad died long before the period of Conquest ~ and, amazingly, the only sources telling anybody he existed were created by the same committee that invented Islam.