Originally Posted by led*
But isn't religion is one the reasons why there is war?
Yes, it can be. Religion is a meme
. That doesn't mean it's a stupid picture on the internet, it's a defined term that describes an idea or concept which replicates itself from person to person, and evolves as it does so.
Religion evolves from animist and totemic spirit reverence into actual spirit worship and eventually the spirits are imbued with greater and greater powers until they become gods, then the gods settle into hierarchies until finally there is a king of the gods, and this may eventually evolve into a single god. Usually at some point there evolves a narrative about the afterlife and about rewards and punishments and successful mutations of the religious meme tend to include a concept of hell, usually the worst of which is reserved for people who don't actually belong to that religion.
Religion improves social cohesion and if a society grows significantly stronger than those around it or if the religious meme is a particularly potent one then it may be adopted by other societies and then spread. A strong enough religion can mutate into one which demands the conversion of its neighbours and thus causes war.