I believe that the cost of war is outrageous. But I also believe that humans constantly make war and prepare for war because they refuse to behave differently enough to avoid war.
While war is horrible in cost of materials and lives, it is glorious in exploit and vanity. Humans seem to me to love it, to desire it, to set themselves up to expect it, despite the knowledge that it is a horrible thing.
I cannot explain this in short time and detail. I do believe, however, that in human history we've learned to avoid and stop many bad things, like slavery and other bad things. Strangely, although some have tried, we have not found a way to stop making war. When people refuse to not make a path to avoid different choices and decisions I believe it is for a reason, that they wish it to continue.
Perhaps I am wrong.