A large society which is separated into two halves based on ancient tradition- lets say Red Clan and Blue Clan.
Red Clan has "X" beliefs, whereas Blue Clan has "Y" beliefs... They are similar beliefs, but in each case, the Red Clan maintains certain folktales which are heretical and historically incorrect to the Blue Clan, and vise versa.
The two clans begin to argue about which folktales are the true history of their people, each clan denounces the other as heretics and betrayers of the heritage of their people, war begins.