You can read the book After the Prophet by Lezley Hazleton. It presents a lucid and readable historical account of how the Shia-Sunni discord happened, from a historical point of view. However, I have two caveats about this book. While written by a Westerner who is apparently not a party to the dispute, the book has appeared to me to be subtly biased in favor of the Shias. Secondly, the doctrinal and cultural differences between Shia and Sunni are perhaps more important in shaping the conflict than any political or historical conflicts. This factor too is inadequately dealt with in the book.

This might deserve it's own thread but I figure I'll ask in case it doesn't.

Where do the praying differences in Shia's vs Muslim come from? I understand that the sllit initially happened due to a leadership dispute but how did it go on to affect how prayer should be completed.