The vast mass of conflict in the world stems from people seeking to impose their beliefs and ways of life on others. The deep tragedy of this battle of beliefs is that there is ultimately no way of proving any one belief to be better than any other.
All beliefs are equally valid.
It's all a matter of your point of view. Convinced that they had found ultimate reality, these people set out to make others accept it. Typically, they ran into people who already had what they claimed was the real universal Truth and it was a different one. So starts a war, revolution, schism, or whatever. The best reason for believing something is that it works for you.