Idea for a book?
Two early modern states go to war over some disputed territory between them, nominally belong to both. It is a stretch of marshy, inundated land at the wide mouth of the river that divides the two countries. Theoretically of value because of the opening on the sea, practically useless because it is nothing but reeds and mazy waterways. Unfortunately the traditional inhabitants of the marsh know it well and have a strong tradition of independence. They lead both armies into disaster and end up, improbably, ruling both countries.