It's simple really. One cannot appreciate something without having known its opposite. If growing up, you are the finest of meals and Frank the best of drinks, you won't know how good your life is until all that is taken away and you are left to live a normal life. The same goes for peace and war. A world that has never known war will find it hard to appreciate peace. Imagine if there had never beenany world war. Trump would have fired missiles on North Korea ages ago. Kim Jong In would have probably done the same. But since we have known war, there is a natural thought to avoid that kind of destruction and death again. That's why it's said, there is no peace without war