Shia Sunni difference is on a very flimsy point. People who were converted by Shias became Shia and people who were converted by Sunnis became Sunnis.
Yet the essence of both sects is very similar. both believe in Allah and Paighambar. Other small differences erupt in every family but so much bloodshed and hatred still exists even out of the history of Islam books. God knows when will it stop. Both sides are strictly adhering to their points and never relenting. Non violence- till now unknown in Islam, only can bring peace when two sides meet and sit and accept the differences of each other.