The section I just finished was all about the four 'rightly guided' caliph's that followed Mohammed.
I found it interesting that almost immediately after Mohammed's death tribes who had joined the ummah under him wanted to break off and go back to being tribes. They hadn't converted to Islam due to religious faith, but for security. They were banding together to protect themselves and to not be left on the outside of the ummah, because the only people the Muslims couldn't raid were members of the ummah.
Abu Bakr (sorry, I keep typing that 'Baker'...) enticed them back by making a policy of raiding the neighbouring peoples outside of Arabia. This had the added benefit of financing the Muslim state, which was especially important since prior to the unification of the Arabian peninsula under Mohammed a good portion of the tribes made their living by raiding one another. The inability to make raids against their own tribe, the ummah, made supporting themselves very difficult. Abu Bakr's policy also enabled him to circumvent the age old issues that Arab tribes people had with 'kings'. They didn't tend to follow a singular leader for long. But as long as Abu Bakr was a war leader, they would follow.
And about the reign of Uthman: "The Qur'an-reciters, who knew the scripture by heart and had become the chief religious authorities, were also incensed when Uthman insisted that only one version of the sacred text be used in the garrison towns, and suppressed variants, which many of them preferred, but which differed in minor details."
She doesn't cite reference on this fact, but it does blatantly state that there were multiple variant texts of the Qur'an in circulation as soon after Mohammed's death as Uthman's reign, which began after Umar was assassinated in 644. So..a little more than ten years after Mohammed's death.