Honestly, not very relevant. There was actually very little dispute over the succession of Abu Bakr and Umar and Uthman. It was during the reign of Uthman that troubles began cropping up, due in no small part to the rapid expansion of the Islamic state and the burgeoning number of new Muslims. If there's one event which we can pinpoint as the impetus for the civil wars it's really the assassination of Uthman. It was in response to his assassination that the two camps of Ali and Muawiyyah arose and this is what set the stage for the civil wars. I wrote a very long post a while back and I'll see if I can dig it up, but really the split between Sunnism and Shi'ism was more of a gradually expanding process than a simple white/black dispute over the succession of Muhammad.

He actually did, but the history is written by those in power.

http://en.wikipedia.org/wiki/Hadith_of_the_pond_of_Khumm

while he declared who would succeed him, and its been narrated in various books. Many muslim do not deny Muhammad’s declaration about Ali as his successor at Ghadir Khumm, but they argue that he was simply urging the audience to hold his cousin and son-in-law in high esteem and affection