Its not only Religion

The world population, even if we consider ancient civilizations, were never homogeneous. There are different kinds of people -- some are different due to their physical appearance (skin colour, height, hair) and some carry mythical (religion, societal belief, rituals) difference. And human societies always classify people based on that difference. Different societies in different parts of the world in different era has been classifying people based on their colour, race, community, language, wealth, assets, profession, religion, caste and so on. If the classification based on religion leads to some conflict, its creates news today.