As brief as I can manage, I am a few months into the writing of my third novel. While I am quite happy with the world I have created and how the characters are developing and intertwining along the way. I am struggling to bring the conflict that I need. I have numerous scenes written for into the war and a clear idea of how to end it. But for the life of me I cannot think of a strong enough reason or state of affairs that would lead to all out war.
I have 6 kingdoms all explained and ready to fight, treaties and rivalries all ready to be enacted and clearly defined partnerships. But war is costly in many different ways, it is also of no benefit other than technological advancement and my characters know this. All it will take is one person to start the whole thing, but I can't find a reason for any of them to do it, from their characters point of view.
So I ask you, the good people of the internet (and in good faith) :)
What would it take for you to be the one who starts a war. Knowing that it will drag every other nation and therefore all its people in with you?
(While the book is set as ancient history - swords, shields, bows, etc. Any ideas would be appreciated.)