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In islamic world, many traditions deal with Heraclius, emperor of Byzantium who ruled this country at the same time Muhammad lived and was considered as a prophet.

http://en.wikipedia.org/wiki/Heraclius#Islamic_view_of_the_Emperor

Let's imagine that the religious tradition depicting him as an admirator of islam was true and he accepted to convert to islam during Muhammad's life... What could have been the consequences of this event ?

In my opinion, I think that Heraclius could be a potential successor to Muhammad at the head of the Umma, mixing in another way the political and religious charges, just like at the time of the Prophet... That could lead to some kind of a global califate, including arabian conquests and eastern roman territories.

What would that be five or six years later, that's the question ;)
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