Religious differences are as old as religion. There is no religion whose history is not rife with bitter disputes between its denominations. Islam is no exception, with the dispute between its biggest branches, Sunnism and Shiism, being almost as old as Islam itself.
In its most extreme form, this dispute, like many other religious conflicts of concepts and beliefs, is presented by both sides as a conflict between truth and falsehood, right and wrong, good and evil, authenticity and distortion. Each party claims its version of Islam to be the real one and positions the other as a distortion and aberration. Fundamentalists on both sides often see the others as misled and misleading. At various places and times in history, this dispute turned bloody. Even today, deadly persecution of Sunni and Shia minorities in places like Iraq and Pakistan remains common.