A war is a clash of wills — a bloody collision between irreconcilable national interests. In the ancient world, it was easy to tell apart winners and losers. The defeated city — think of Troy in the “Iliad” — was looted and burned to the ground. Most of the population was put to the sword, while the young women were distributed as bonus prizes among the winners. One of the epithets Homer uses for the hero Odysseus is “sacker of cities.” Homer meant this as a compliment. Modern wars, on the other hand, can be hugely complicated affairs. Sometimes, the…