Violence is as prevalent among "religious" people as it is among non-religious people because fear is at the core of both sectors. Humans want to control things; one another, society, situations, money, and even God. That is why even though a religion dictates peace in its text, it does not demonstrate peace in the actions of its followers.
Muhammad used the facade of unifying the tribes as a basis to ultimately control what people believed about God. Judaism with its legalistic rules for living does the same thing by trying to control how people conduct their lives. Christianity, as it stems from Roman Catholic roots, is no different and in fact, has the most violent historical approach to conforming the masses to a single belief system. You do remember the Crusades, don’t you?