UNIFIED RULES FOR CLAN WARS

I read everything here, and I still don't understand what reasons there could be for declaring war?

There are many different reasons – from dislike of a particular person from a particular clan to intense hatred of the clan (you might say that there is no such thing on the forum, and everyone loves each other, but that's not true; they just keep quiet).
If someone insults someone else, that's also a good reason for war. But I don't think anyone will declare war without a reason. People are like that – they will always find a reason if one is needed.