This is a rather complicated way of stating that war is a negative sum game. The total wealth and output of both sides will always be lower afterwards. In less interdependent days, the victor could sometimes still come out ahead economically. Now, with the interdependence of the modern world, that is impossible. God bless free trade; it's the best enforcer of world peace in history.

After a discussion with Uberfetus, I'd like to expand on my point a bit. War is, in the modern world, always an economic loss. However, that does not mean war is never justifiable. There are times when the alternatives are worse, such as when national survival is at stake or when one side is behaving in a genocidal or otherwise monstrous fashion. There are certainly things worse than war, and in that sense a war can have a winner. Otherwise, war is a losing strategy.