The general idea is interesting, but the story itself suffers a lot from cheap drama coming from nearly all characters' clinical idiocy.
Like, wearing the attackers down with defensive strategy is not some stroke of pure genius beyond mere mortals' ken. It's the most common and obvious strategem in the entire military history. Sun Tzu warned against falling into that trap 25 centuries ago. It's kinda hilarious watching all those military advisors stutter in disbelief over what should've been the kingdom's first choice from the very beginning.